Journal articles on the topic 'HIV; capsid; core stability'
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Guedán, Anabel, Callum D. Donaldson, Eve R. Caroe, Ophélie Cosnefroy, Ian A. Taylor, and Kate N. Bishop. "HIV-1 requires capsid remodelling at the nuclear pore for nuclear entry and integration." PLOS Pathogens 17, no. 9 (September 20, 2021): e1009484. http://dx.doi.org/10.1371/journal.ppat.1009484.
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The capsid (CA) lattice of the HIV-1 core plays a key role during infection. From the moment the core is released into the cytoplasm, it interacts with a range of cellular factors that, ultimately, direct the pre-integration complex to the integration site. For integration to occur, the CA lattice must disassemble. Early uncoating or a failure to do so has detrimental effects on virus infectivity, indicating that an optimal stability of the viral core is crucial for infection. Here, we introduced cysteine residues into HIV-1 CA in order to induce disulphide bond formation and engineer hyper-stable mutants that are slower or unable to uncoat, and then followed their replication. From a panel of mutants, we identified three with increased capsid stability in cells and found that, whilst the M68C/E212C mutant had a 5-fold reduction in reverse transcription, two mutants, A14C/E45C and E180C, were able to reverse transcribe to approximately WT levels in cycling cells. Moreover, these mutants only had a 5-fold reduction in 2-LTR circle production, suggesting that not only could reverse transcription complete in hyper-stable cores, but that the nascent viral cDNA could enter the nuclear compartment. Furthermore, we observed A14C/E45C mutant capsid in nuclear and chromatin-associated fractions implying that the hyper-stable cores themselves entered the nucleus. Immunofluorescence studies revealed that although the A14C/E45C mutant capsid reached the nuclear pore with the same kinetics as wild type capsid, it was then retained at the pore in association with Nup153. Crucially, infection with the hyper-stable mutants did not promote CPSF6 re-localisation to nuclear speckles, despite the mutant capsids being competent for CPSF6 binding. These observations suggest that hyper-stable cores are not able to uncoat, or remodel, enough to pass through or dissociate from the nuclear pore and integrate successfully. This, is turn, highlights the importance of capsid lattice flexibility for nuclear entry. In conclusion, we hypothesise that during a productive infection, a capsid remodelling step takes place at the nuclear pore that releases the core complex from Nup153, and relays it to CPSF6, which then localises it to chromatin ready for integration.
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Forshey, Brett M., Uta von Schwedler, Wesley I. Sundquist, and Christopher Aiken. "Formation of a Human Immunodeficiency Virus Type 1 Core of Optimal Stability Is Crucial for Viral Replication." Journal of Virology 76, no. 11 (June 1, 2002): 5667–77. http://dx.doi.org/10.1128/jvi.76.11.5667-5677.2002.
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ABSTRACT Virions of human immunodeficiency virus type 1 (HIV-1) and other lentiviruses contain conical cores consisting of a protein shell composed of the viral capsid protein (CA) surrounding an internal viral ribonucleoprotein complex. Although genetic studies have implicated CA in both early and late stages of the virus replication cycle, the mechanism of core disassembly following penetration of target cells remains undefined. Using quantitative assays for analyzing HIV-1 core stability in vitro, we identified point mutations in CA that either reduce or increase the stability of the HIV-1 core without impairing conical core formation in virions. Alterations in core stability resulted in severely attenuated HIV-1 replication and impaired reverse transcription in target cells with only minimal effects on viral DNA synthesis in permeabilized virions in vitro. We conclude that formation of a viral core of optimal stability is a prerequisite for efficient HIV-1 infection and suggest that disassembly of the HIV-1 core is a regulated step in infection that may be an attractive target for pharmacologic intervention.
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Schommers, P., G. Martrus, U. Matschl, M. Sirignano, M. Lütgehetmann, L. Richert, T. J. Hope, G. Fätkenheuer, and M. Altfeld. "Changes in HIV-1 Capsid Stability Induced by Common Cytotoxic-T-Lymphocyte-Driven Viral Sequence Mutations." Journal of Virology 90, no. 16 (June 8, 2016): 7579–86. http://dx.doi.org/10.1128/jvi.00867-16.
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ABSTRACTHIV-1-infected individuals with protective HLA class I alleles exhibit better control of viremia and slower disease progression. Virus control in these individuals has been associated with strong and potent HIV-1-specific cytotoxic-T-lymphocyte (CTL) responses restricted by protective HLA alleles, but control of viremia also occurs in the presence of selected CTL escape mutations. CTL escape mutations restricted by protective HLA class I molecules are frequently located in the conserved p24 Gag sequence of HIV-1 that encodes the conical capsid core and have been suggested to reduce viral replication capacity. In this study, the consequences of well-described CTL-associated p24 Gag sequence mutations for HIV-1 capsid stability were assessed using a cyclosporine (CsA) washout assay. The frequently occurring HLA-B57- and HLA-B27-associated CTL escape mutations T242N and R264K resulted in delayed capsid uncoating, suggesting modulation of capsid stability. The described compensatory mutations L268M and S173A observed in R264K viruses reconstituted the capsid-uncoating half-time. Interestingly, capsid stability was correlated with infectivity. Taken together, these data demonstrate that CTL-driven escape mutations within p24 Gag restricted by protective HLA class I alleles have a significant impact on capsid stability that might contribute to the persistent control of viral replication observed despite viral escape from CTL responses.IMPORTANCESequence mutations within p24 Gag selected by CTL responses restricted by protective HLA class I alleles have been associated with reduced viral fitness. However, the precise mechanisms underlying the reduced viral replication capacity and lower viral loads associated with these mutations remain unclear. Here, we demonstrate that dominant HLA-B27-associated CTL escape mutations within HIV-1 capsid lead to enhanced capsid rigidity, providing a possible mechanism for the reduced viral fitness of these variants.
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Newman, Margaret, Pong Kian Chua, Fan-Mei Tang, Pei-Yi Su, and Chiaho Shih. "Testing an Electrostatic Interaction Hypothesis of Hepatitis B Virus Capsid Stability by Using an In Vitro Capsid Disassembly/Reassembly System." Journal of Virology 83, no. 20 (August 5, 2009): 10616–26. http://dx.doi.org/10.1128/jvi.00749-09.
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ABSTRACT To test a previously coined “charge balance hypothesis” of human hepatitis B virus (HBV) capsid stability, we established an in vitro disassembly and reassembly system using bacterially expressed HBV capsids. Capsid disassembly can be induced by micrococcal nuclease digestion of encapsidated RNA. HBV core protein (HBc) mutants containing various amounts of arginine were constructed by serial truncations at the C terminus. Capsids containing smaller amounts of arginine (HBc 149, 154, and 157) remained intact after micrococcal nuclease digestion by native gel electrophoresis. Capsids containing larger amounts of arginine (HBc 159, 164, 169, and 171) exhibited reduced and more diffuse banding intensity and slightly upshifted mobility (HBc 159 and 164). Capsids containing the largest amounts of arginine (HBc 173, 175, and 183), as well as HBc 167, exhibited no detectable banding signal, indicating loss of capsid integrity or stability. Interestingly, capsid reassembly can be induced by polyanions, including oligonucleotides, poly-glutamic acid, and nonbiological polymer (polyacrylic acid). In contrast, polycations (polylysine and polyethylenimine) and low-molecular-weight anions (inositol triphosphate) induced no capsid reassembly. Results obtained by gel assay were confirmed by electron microscopy. Reassembled capsids comigrated with undigested parental capsids on agarose gels and cosedimented with undigested capsids by sucrose gradient ultracentrifugation. Taken together, the results indicate that HBV capsid assembly and integrity depend on polyanions, which probably can help minimize intersubunit charge repulsion caused mainly by arginine-rich domain III or IV in close contact. The exact structure of polyanions is not important for in vitro capsid reassembly. A large amount of independent experimental evidence for this newly coined “electrostatic interaction hypothesis” is discussed.
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Forshey, Brett M., and Christopher Aiken. "Disassembly of Human Immunodeficiency Virus Type 1 Cores In Vitro Reveals Association of Nef with the Subviral Ribonucleoprotein Complex." Journal of Virology 77, no. 7 (April 1, 2003): 4409–14. http://dx.doi.org/10.1128/jvi.77.7.4409-4414.2003.
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ABSTRACT The human immunodeficiency virus type 1 (HIV-1) virulence factor Nef enhances viral infectivity in single-cycle infection assays and accelerates HIV-1 replication in vitro. It has been reported that the effects of Nef are mediated early after viral entry and before the completion of reverse transcription, as viral DNA synthesis is strongly attenuated during infection by Nef-defective virions. Our previous work has demonstrated that Nef is associated with mature HIV-1 cores, implicating Nef in the regulation of HIV-1 core stability. Here we report a comparative analysis of HIV-1 cores isolated from wild-type and Nef-defective particles. We observed no effect of Nef on HIV-1 core structure or stability; however, Nef cosedimented with a subviral ribonucleoprotein complex following dissociation of CA. These results indicate that Nef interacts tightly with an internal component of the HIV-1 core. They further suggest that virion-associated Nef may facilitate an early step in HIV-1 infection following dissociation of the viral capsid in the target cell.
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Newman, Margaret, Fat-Moon Suk, Maria Cajimat, Pong Kian Chua, and Chiaho Shih. "Stability and Morphology Comparisons of Self-AssembledVirus-Like Particles from Wild-Type and Mutant Human Hepatitis B VirusCapsidProteins." Journal of Virology 77, no. 24 (December 15, 2003): 12950–60. http://dx.doi.org/10.1128/jvi.77.24.12950-12960.2003.
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ABSTRACT Instead of displaying the wild-type selective export of virions containing mature genomes, human hepatitis B virus (HBV) mutant I97L, changing from an isoleucine to a leucine at amino acid 97 of HBV core antigen (HBcAg), lost the high stringency of selectivity in genome maturity during virion export. To understand the structural basis of this so-called “immature secretion” phenomenon, we compared the stability and morphology of self-assembled capsid particles from the wild-type and mutant I97L HBV, in either full-length (HBcAg1-183) or truncated core protein contexts (HBcAg1-149 and HBcAg1-140). Using negative staining and electron microscopy, full-length particles appear as “thick-walled” spherical particles with little interior space, whereas truncated particles appear as“ thin-walled” spherical particles with a much larger inner space. We found no significant differences in capsid stability between wild-type and mutant I97L particles under denaturing pH and temperature in either full-length or truncated core protein contexts. In general, HBV capsid particles (HBcAg1-183, HBcAg1-149, and HBcAg1-140) are very robust but will dissociate at pH 2 or 14, at temperatures higher than 75°C, or in 0.1% sodium dodecyl sulfate (SDS). An unexpected upshift banding pattern of the SDS-treated full-length particles during agarose gel electrophoresis is most likely caused by disulfide bonding of the last cysteine of HBcAg. HBV capsids are known to exist in natural infection as dimorphic T=3 or T=4 icosahedral particles. No difference in the ratio between T=3 (78%) and T=4 particles (20.3%) are found between wild-type HBV and mutant I97L in the context of HBcAg1-140. In addition, we found no difference in capsid stability between T=3 and T=4 particles successfully separated by using a novel agarose gel electrophoresis procedure.
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Kang, Hang, Jaehoon Yu, and Guhung Jung. "Phosphorylation of hepatitis B virus core C-terminally truncated protein (Cp149) by PKC increases capsid assembly and stability." Biochemical Journal 416, no. 1 (October 28, 2008): 47–54. http://dx.doi.org/10.1042/bj20080724.
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The HBV (hepatitis B virus) core is a phosphoprotein whose assembly, replication, encapsidation and localization are regulated by phosphorylation. It is known that PKC (protein kinase C) regulates pgRNA (pregenomic RNA) encapsidation by phosphorylation of the C-terminus of core, which is a component packaged into capsid. Neither the N-terminal residue phosphorylated by PKC nor the role of the C-terminal phosphorylation have been cleary defined. In the present study we found that HBV Cp149 (core protein C-terminally truncated at amino acid 149) expressed in Escherichia coli was phosphorylated by PKC at Ser106. PKC-mediated phosphorylation increased core affinity, as well as assembly and capsid stability. In vitro phosphorylation with core mutants (S26A, T70A, S106A and T114A) revealed that the Ser106 mutation inhibited phosphorylation of core by PKC. CD analysis also revealed that PKC-mediated phosphorylation stabilized the secondary structure of capsid. When either pCMV/FLAG-Cp149[WT (wild-type)] or pCMV/FLAG-S106A Cp149 was transfected into Huh7 human hepatoma cells, mutant capsid level was decreased by 2.06-fold with the S106A mutant when compared with WT, although the same level of total protein was expressed in both cases. In addition, when pUC1.2x and pUC1.2x/S106A were transfected, mutant virus titre was decreased 2.31-fold compared with WT virus titre. In conclusion, PKC-mediated phosphorylation increased capsid assembly, stability and structural stability.
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Leschonsky, Bernd, Christine Ludwig, Kurt Bieler, and Ralf Wagner. "Capsid stability and replication of human immunodeficiency virus type 1 are influenced critically by charge and size of Gag residue 183." Journal of General Virology 88, no. 1 (January 1, 2007): 207–16. http://dx.doi.org/10.1099/vir.0.81894-0.
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Structural data support a model where – following proteolytic cleavage – the amino-terminal domain of human immunodeficiency virus type 1 (HIV-1) capsid protein refolds into a β-hairpin/helix tertiary structure that is stabilized by a buried salt bridge forming between the positively charged primary imino group of a proline residue and the negatively charged carboxyl group of a conserved aspartate. In order to evaluate the contribution of either side-chain length or charge to the formation of infectious virus capsids, aspartate 183 was substituted for glutamate or asparagine in the viral context. It was found that both modifications abolished infectivity of the corresponding viruses in permissive T lymphocytes, although none of particle assembly and release, RNA encapsidation, incorporation of Env glycoproteins and packaging of cyclophilin A were impaired. However, whereas biophysical analyses of mutant virions yielded wild-type-like particle sizes and densities, electron microscopy revealed aberrant core morphologies that could be attributed to either increased (D183N) or reduced (D183E) capsid stability. Although the two amino acid substitutions had opposing effects upon core stability, both mutants were shown to exhibit a severe block in early reverse transcription, underscoring the importance of correct salt-bridge formation for early steps of virus replication.
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Briones, Marisa S., Charles W. Dobard, and Samson A. Chow. "Role of Human Immunodeficiency Virus Type 1 Integrase in Uncoating of the Viral Core." Journal of Virology 84, no. 10 (March 10, 2010): 5181–90. http://dx.doi.org/10.1128/jvi.02382-09.
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ABSTRACT After membrane fusion with a target cell, the core of human immunodeficiency virus type 1 (HIV-1) enters into the cytoplasm, where uncoating occurs. The cone-shaped core is composed of the viral capsid protein (CA), which disassembles during uncoating. The underlying factors and mechanisms governing uncoating are poorly understood. Several CA mutations can cause changes in core stability and a block at reverse transcription, demonstrating the requirement for optimal core stability during viral replication. HIV-1 integrase (IN) catalyzes the insertion of the viral cDNA into the host genome, and certain IN mutations are pleiotropic. Similar to some CA mutants, two IN mutants, one with a complete deletion of IN (NL-ΔIN) and the other with a Cys-to-Ser substitution (NL-C130S), were noninfectious, with a replication block at reverse transcription. Compared to the wild type (WT), the cytoplasmic CA levels of the IN mutants in infected cells were reduced, suggesting accelerated uncoating. The role of IN during uncoating was examined by isolating and characterizing cores from NL-ΔIN and NL-C130S. Both IN mutants could form functional cores, but the core yield and stability were decreased. Also, virion incorporation of cyclophilin A (CypA), a cellular peptidyl-prolyl isomerase that binds specifically to CA, was decreased in the IN mutants. Cores isolated from WT virus depleted of CypA had an unstable-core phenotype, confirming a role of CypA in promoting optimal core stability. Taken together, our results indicate that IN is required during uncoating for maintaining CypA-CA interaction, which promotes optimal stability of the viral core.
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Welker, Reinhold, Heinrich Hohenberg, Uwe Tessmer, Carola Huckhagel, and Hans-Georg Kräusslich. "Biochemical and Structural Analysis of Isolated Mature Cores of Human Immunodeficiency Virus Type 1." Journal of Virology 74, no. 3 (February 1, 2000): 1168–77. http://dx.doi.org/10.1128/jvi.74.3.1168-1177.2000.
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ABSTRACT Mature human immunodeficiency virus type 1 (HIV-1) particles contain a cone-shaped core structure consisting of the internal ribonucleoprotein complex encased in a proteinaceous shell derived from the viral capsid protein. Because of their very low stability after membrane removal, HIV-1 cores have not been purified in quantities sufficient for structural and biochemical analysis. Based on our in vitro assembly experiments, we have developed a novel method for isolation of intact mature HIV-1 cores. Concentrated virus suspensions were briefly treated with nonionic detergent and immediately centrifuged in a microcentrifuge for short periods of time. The resuspended pellet was subsequently analyzed by negative-stain and thin-section electron microscopy and by immunoelectron microscopy. Abundant cone-shaped cores as well as tubular and aberrant structures were observed. Stereo images showed that core structures preserved their three-dimensional architecture and exhibited a regular substructure. Detailed analysis of 155 cores revealed an average length of ca. 103 nm, an average diameter at the base of ca. 52 nm, and an average angle of 21.3°. There was significant variability in all parameters, indicating that HIV cores are not homogeneous. Immunoblot analysis of core preparations allowed semiquantitative estimation of the relative amounts of viral and cellular proteins inside the HIV-1 core, yielding a model for the topology of various proteins inside the virion.
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Eschbach, Jenna E., Jennifer L. Elliott, Wen Li, Kaneil K. Zadrozny, Keanu Davis, Shawn J. Mohammed, Dana Q. Lawson, Owen Pornillos, Alan N. Engelman, and Sebla B. Kutluay. "Capsid Lattice Destabilization Leads to Premature Loss of the Viral Genome and Integrase Enzyme during HIV-1 Infection." Journal of Virology 95, no. 2 (October 28, 2020): e00984-20. http://dx.doi.org/10.1128/jvi.00984-20.
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ABSTRACTThe human immunodeficiency virus type 1 (HIV-1) capsid (CA) protein forms a conical lattice around the viral ribonucleoprotein complex (vRNP) consisting of a dimeric viral genome and associated proteins, together constituting the viral core. Upon entry into target cells, the viral core undergoes a process termed uncoating, during which CA molecules are shed from the lattice. Although the timing and degree of uncoating are important for reverse transcription and integration, the molecular basis of this phenomenon remains unclear. Using complementary approaches, we assessed the impact of core destabilization on the intrinsic stability of the CA lattice in vitro and fates of viral core components in infected cells. We found that substitutions in CA can impact the intrinsic stability of the CA lattice in vitro in the absence of vRNPs, which mirrored findings from an assessment of CA stability in virions. Altering CA stability tended to increase the propensity to form morphologically aberrant particles, in which the vRNPs were mislocalized between the CA lattice and the viral lipid envelope. Importantly, destabilization of the CA lattice led to premature dissociation of CA from vRNPs in target cells, which was accompanied by proteasomal-independent losses of the viral genome and integrase enzyme. Overall, our studies show that the CA lattice protects the vRNP from untimely degradation in target cells and provide the mechanistic basis of how CA stability influences reverse transcription.IMPORTANCE The human immunodeficiency virus type 1 (HIV-1) capsid (CA) protein forms a conical lattice around the viral RNA genome and the associated viral enzymes and proteins, together constituting the viral core. Upon infection of a new cell, viral cores are released into the cytoplasm where they undergo a process termed “uncoating,” i.e., shedding of CA molecules from the conical lattice. Although proper and timely uncoating has been shown to be important for reverse transcription, the molecular mechanisms that link these two events remain poorly understood. In this study, we show that destabilization of the CA lattice leads to premature dissociation of CA from viral cores, which exposes the viral genome and the integrase enzyme for degradation in target cells. Thus, our studies demonstrate that the CA lattice protects the viral ribonucleoprotein complexes from untimely degradation in target cells and provide the first causal link between how CA stability affects reverse transcription.
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Rasool, Nouman, and Waqar Hussain. "Three Major Phosphoacceptor Sites in HIV-1 Capsid Protein Enhances its Structural Stability and Resistance Against the Inhibitor: Explication Through Molecular Dynamics Simulation, Molecular Docking and DFT Analysis." Combinatorial Chemistry & High Throughput Screening 23, no. 1 (March 16, 2020): 41–54. http://dx.doi.org/10.2174/1386207323666191213142223.
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Background: Human Immunodeficiency Virus 1 (HIV-1) is a lentivirus, which causes various HIV-associated infections. The HIV-1 core dissociation is essential for viral cDNA synthesis and phosphorylation of HIV-1 capsid protein (HIV-1 CA) plays an important role in it. Objective: The aim of this study was to explicate the role of three phosphoserine sites i.e. Ser109, Ser149 and Ser178 in the structural stability of HIV-1 CA, and it’s binding with GS-CA1, a novel potent inhibitor. Method: Eight complexes were analyzed and Molecular Dynamics (MD) simulations were performed to observe the stability of HIV-1 CA in the presence and absence of phosphorylation of serine residues at four different temperatures i.e. 300K, 325K, 340K and 350K, along with molecular docking and DFT analysis. Results: The structures showed maximum stability in the presence of phosphorylated serine residue. However, GS-CA1 docked most strongly with the native structure of HIV-1 CA i.e. binding affinity was -8.5 kcal/mol (Ki = 0.579 µM). Conclusion: These results suggest that the phosphorylation of these three serine residues weakens the binding of GS-CA1 with CA and casts derogatory effect on inhibition potential of this inhibitor, but it supports the stability of HIV-1 CA structure that can enhance regulation and replication of HIV-1 in host cells.
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Le Pogam, Sophie, Pong Kian Chua, Margaret Newman, and Chiaho Shih. "Exposure of RNA Templates and Encapsidation of Spliced Viral RNA Are Influenced by the Arginine-Rich Domain of Human Hepatitis B Virus Core Antigen (HBcAg 165-173)." Journal of Virology 79, no. 3 (February 1, 2005): 1871–87. http://dx.doi.org/10.1128/jvi.79.3.1871-1887.2005.
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ABSTRACT Previously, human hepatitis B virus (HBV) mutant 164, which has a truncation at the C terminus of the HBV core antigen (HBcAg), was speculated to secrete immature genomes. For this study, we further characterized mutant 164 by different approaches. In addition to the 3.5-kb pregenomic RNA (pgRNA), the mutant preferentially encapsidated the 2.2-kb or shorter species of spliced RNA, which can be reverse transcribed into double-stranded DNA before virion secretion. We observed that mutant 164 produced less 2.2-kb spliced RNA than the wild type. Furthermore, it appeared to produce at least two different populations of capsids: one encapsidated a nuclease-sensitive 3.5-kb pgRNA while the other encapsidated a nuclease-resistant 2.2-kb spliced RNA. In contrast, the wild-type core-associated RNA appeared to be resistant to nuclease. When arginines and serines were systematically restored at the truncated C terminus, the core-associated DNA and nuclease-resistant RNA gradually increased in both size and signal intensity. Full protection of encapsidated pgRNA from nuclease was observed for HBcAg 1-171. A full-length positive-strand DNA phenotype requires positive charges at amino acids 172 and 173. Phosphorylation at serine 170 is required for optimal RNA encapsidation and a full-length positive-strand DNA phenotype. RNAs encapsidated in Escherichia coli by capsids of HBcAg 154, 164, and 167, but not HBcAg 183, exhibited nuclease sensitivity; however, capsid instability after nuclease treatment was observed only for HBcAg 164 and 167. A new hypothesis is proposed here to highlight the importance of a balanced charge density for capsid stability and intracapsid anchoring of RNA templates.
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Selzer, Lisa, Sarah Katen, and Adam Zlotnick. "A Disulfide in HBV Core Protein Dimer Allosterically Modifies Capsid Assembly and Stability." Biophysical Journal 106, no. 2 (January 2014): 60a. http://dx.doi.org/10.1016/j.bpj.2013.11.413.
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Hope, R. Graham, and John McLauchlan. "Sequence motifs required for lipid droplet association and protein stability are unique to the hepatitis C virus core protein." Journal of General Virology 81, no. 8 (August 1, 2000): 1913–25. http://dx.doi.org/10.1099/0022-1317-81-8-1913.
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From analysis of the primary sequence of the hepatitis C virus (HCV) core protein, we have identified three separable regions based on hydrophobicity and clustering of basic amino acids within the protein. Comparison with capsid proteins of related pesti- and flaviviruses suggested that HCV core has a unique central domain (domain 2). Previous findings have revealed that core protein can associate with lipid droplets which are intracellular storage sites for triacylglycerols and cholesterol esters. Confocal analysis of variant forms lacking regions of core indicated that most residues within the unique region are necessary for association of the protein with lipid droplets. A segment within domain 2 (from residues 125 to 144) also was required for stability of the protein and a polypeptide lacking these sequences was degraded apparently by the proteasome. In cells depleted of lipid droplets, core protein remained located in the cytoplasm. Moreover, cleavage of the protein at the maturation site and stability were not affected by inability to bind to lipid droplets.
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Jiang, Jiyang, Sherimay D. Ablan, Suchitra Derebail, Kamil Hercík, Ferri Soheilian, James A. Thomas, Shixing Tang, et al. "The interdomain linker region of HIV-1 capsid protein is a critical determinant of proper core assembly and stability." Virology 421, no. 2 (December 2011): 253–65. http://dx.doi.org/10.1016/j.virol.2011.09.012.
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Shehu-Xhilaga, M., H. G. Kraeusslich, S. Pettit, R. Swanstrom, J. Y. Lee, J. A. Marshall, S. M. Crowe, and J. Mak. "Proteolytic Processing of the P2/Nucleocapsid Cleavage Site Is Critical for Human Immunodeficiency Virus Type 1 RNA Dimer Maturation." Journal of Virology 75, no. 19 (October 1, 2001): 9156–64. http://dx.doi.org/10.1128/jvi.75.19.9156-9164.2001.
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ABSTRACT Differences in virion RNA dimer stability between mature and protease-defective (immature) forms of human immunodeficiency virus type 1 (HIV-1) suggest that maturation of the viral RNA dimer is regulated by the proteolytic processing of the HIV-1 Gag and Gag-Pol precursor proteins. However, the proteolytic processing of these proteins occurs in several steps denoted primary, secondary, and tertiary cleavage events and, to date, the processing step associated with formation of stable HIV-1 RNA dimers has not been identified. We show here that a mutation in the primary cleavage site (p2/nucleocapsid [NC]) hinders formation of stable virion RNA dimers, while dimer stability is unaffected by mutations in the secondary (matrix/capsid [CA], p1/p6) or a tertiary cleavage site (CA/p2). By introducing mutations in a shared cleavage site of either Gag or Gag-Pol, we also show that the cleavage of the p2/NC site in Gag is more important for dimer formation and stability than p2/NC cleavage in Gag-Pol. Electron microscopy analysis of viral particles shows that mutations in the primary cleavage site in Gag but not in Gag-Pol inhibit viral particle maturation. We conclude that virion RNA dimer maturation is dependent on proteolytic processing of the primary cleavage site and is associated with virion core formation.
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Tan, Zhenning, Karolyn Pionek, Nuruddin Unchwaniwala, Megan L. Maguire, Daniel D. Loeb, and Adam Zlotnick. "The Interface between Hepatitis B Virus Capsid Proteins Affects Self-Assembly, Pregenomic RNA Packaging, and Reverse Transcription." Journal of Virology 89, no. 6 (January 7, 2015): 3275–84. http://dx.doi.org/10.1128/jvi.03545-14.
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ABSTRACTHepatitis B virus (HBV) capsid proteins (Cps) assemble around the pregenomic RNA (pgRNA) and viral reverse transcriptase (P). pgRNA is then reverse transcribed to double-stranded DNA (dsDNA) within the capsid. The Cp assembly domain, which forms the shell of the capsid, regulates assembly kinetics and capsid stability. The Cp, via its nucleic acid-binding C-terminal domain, also affects nucleic acid organization. We hypothesize that the structure of the capsid may also have a direct effect on nucleic acid processing. Using structure-guided design, we made a series of mutations at the interface between Cp subunits that change capsid assembly kinetics and thermodynamics in a predictable manner. Assembly in cell culture mirroredin vitroactivity. However, all of these mutations led to defects in pgRNA packaging. The amount of first-strand DNA synthesized was roughly proportional to the amount of RNA packaged. However, the synthesis of second-strand DNA, which requires two template switches, was not supported by any of the substitutions. These data demonstrate that the HBV capsid is far more than an inert container, as mutations in the assembly domain, distant from packaged nucleic acid, affect reverse transcription. We suggest that capsid molecular motion plays a role in regulating genome replication.IMPORTANCEThe hepatitis B virus (HBV) capsid plays a central role in the virus life cycle and has been studied as a potential antiviral target. The capsid protein (Cp) packages the viral pregenomic RNA (pgRNA) and polymerase to form the HBV core. The role of the capsid in subsequent nucleic acid metabolism is unknown. Here, guided by the structure of the capsid with bound antiviral molecules, we designed Cp mutants that enhanced or attenuated the assembly of purified Cpin vitro. In cell culture, assembly of mutants was consistent with theirin vitrobiophysical properties. However, all of these mutations inhibited HBV replication. Specifically, changing the biophysical chemistry of Cp caused defects in pgRNA packaging and synthesis of the second strand of DNA. These results suggest that the HBV Cp assembly domain potentially regulates reverse transcription, extending the activities of the capsid protein beyond its presumed role as an inert compartment.
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Lai, Vicky C. H., Weidong Zhong, Angela Skelton, Paul Ingravallo, Venteislav Vassilev, Ruben O. Donis, Zhi Hong, and Johnson Y. N. Lau. "Generation and Characterization of a Hepatitis C Virus NS3 Protease-Dependent Bovine Viral Diarrhea Virus." Journal of Virology 74, no. 14 (July 15, 2000): 6339–47. http://dx.doi.org/10.1128/jvi.74.14.6339-6347.2000.
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ABSTRACT Unique to pestiviruses, the N-terminal protein encoded by the bovine viral diarrhea virus (BVDV) genome is a cysteine protease (Npro) responsible for a self-cleavage that releases the N terminus of the core protein (C). This unique protease is dispensable for viral replication, and its coding region can be replaced by a ubiquitin gene directly fused in frame to the core. To develop an antiviral assay that allows the assessment of anti-hepatitis C virus (HCV) NS3 protease inhibitors, a chimeric BVDV in which the coding region of Npro was replaced by that of an NS4A cofactor-tethered HCV NS3 protease domain was generated. This cofactor-tethered HCV protease domain was linked in frame to the core protein of BVDV through an HCV NS5A-NS5B junction site and mimicked the proteolytic function of Npro in the release of BVDV core for capsid assembly. A similar chimeric construct was built with an inactive HCV NS3 protease to serve as a control. Genomic RNA transcripts derived from both chimeric clones, PH/B(wild-type HCV NS3 protease) and PH/B(S139A) (mutant HCV NS3 protease) were then transfected into bovine cells (MDBK). Only the RNA transcripts from the PH/B clone yielded viable viruses, whereas the mutant clone, PH/B(S139A), failed to produce any signs of infection, suggesting that the unprocessed fusion protein rendered the BVDV core protein defective in capsid assembly. Like the wild-type BVDV (NADL), the chimeric virus was cytopathic and formed plaques on the cell monolayer. Sequence and biochemical analyses confirmed the identity of the chimeric virus and further revealed variant viruses due to growth adaptation. Growth analysis revealed comparable replication kinetics between the wild-type and the chimeric BVDVs. Finally, to assess the genetic stability of the chimeric virus, an Npro-null BVDV (BVDV−Npro in which the entire Npro coding region was deleted) was produced. Although cytopathic, BVDV−Npro was highly defective in viral replication and growth, a finding consistent with the observed stability of the chimeric virus after serial passages.
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Tang, Shixing, Tsutomu Murakami, Beth E. Agresta, Stephen Campbell, Eric O. Freed, and Judith G. Levin. "Human Immunodeficiency Virus Type 1 N-Terminal Capsid Mutants That Exhibit Aberrant Core Morphology and Are Blocked in Initiation of Reverse Transcription in Infected Cells." Journal of Virology 75, no. 19 (October 1, 2001): 9357–66. http://dx.doi.org/10.1128/jvi.75.19.9357-9366.2001.
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ABSTRACT A group of conserved hydrophobic residues faces the interior of the coiled-coil-like structure within the N-terminal domain of the human immunodeficiency virus type 1 (HIV-1) capsid protein (CA). It has been suggested that these residues are important for maintaining stable structure and functional activity. To investigate this possibility, we constructed two HIV-1 clones, in which Trp23 or Phe40 was changed to Ala. We also constructed a third mutant, D51A, which has a mutation that destroys a salt bridge between Pro1 and Asp51. All three mutants are replication defective but produce virus particles. Mutant virions contain all of the viral proteins, although the amount and stability of CA are decreased and levels of virion-associated integrase are reduced. The mutations do not affect endogenous reverse transcriptase activity; however, the mutants are blocked in their ability to initiate reverse transcription in infected cells and no minus-strand strong-stop DNA is detected. The defect in reverse transcription is associated with striking defects in the morphology of mutant virus cores, as determined by transmission electron microscopy. Our data indicate that the mutations made in this study disrupt CA structure and prevent proper maturation of virus cores. We propose that this results in a defect in core stability or in an early postentry event preceding reverse transcription.
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Obr, Martin, Florian K. M. Schur, and Robert A. Dick. "A Structural Perspective of the Role of IP6 in Immature and Mature Retroviral Assembly." Viruses 13, no. 9 (September 17, 2021): 1853. http://dx.doi.org/10.3390/v13091853.
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The small cellular molecule inositol hexakisphosphate (IP6) has been known for ~20 years to promote the in vitro assembly of HIV-1 into immature virus-like particles. However, the molecular details underlying this effect have been determined only recently, with the identification of the IP6 binding site in the immature Gag lattice. IP6 also promotes formation of the mature capsid protein (CA) lattice via a second IP6 binding site, and enhances core stability, creating a favorable environment for reverse transcription. IP6 also enhances assembly of other retroviruses, from both the Lentivirus and the Alpharetrovirus genera. These findings suggest that IP6 may have a conserved function throughout the family Retroviridae. Here, we discuss the different steps in the viral life cycle that are influenced by IP6, and describe in detail how IP6 interacts with the immature and mature lattices of different retroviruses.
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Majeau, Nathalie, Marilène Bolduc, Jean-Baptiste Duvignaud, Rémi Fromentin, and Denis Leclerc. "Effect of cAMP-dependent protein kinase A (PKA) on HCV nucleocapsid assembly and degradation." Biochemistry and Cell Biology 85, no. 1 (February 2007): 78–87. http://dx.doi.org/10.1139/o06-195.
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The primary function of the hepatitis C virus (HCV) core protein is genome encapsidation. Core protein is also subject to post-translational modifications that can impact on the assembly process. In this report, we have studied the effect of cAMP-dependent protein kinase A (PKA) phosphorylation on its assembly and stability in a yeast Pichia pastoris expression system. We have recently shown that co-expression of the human signal peptide peptidase and core protein (amino acids 1–191) in yeast leads to the formation of nucleocapsid-like particles (NLPs) that are morphologically similar to the wild-type HCV capsid. In this system, we expressed mutants S53A and S116A and mutants S53D and S116D to abolish or mimic PKA phosphorylation, respectively. None of these mutations affected HCV assembly, but S116D led to the degradation of core protein. We also showed that nonenveloped NLPs were labelled in vitro by PKA, suggesting that the phosphorylation sites are available at the surface of the NLPs. The co-expression of human PKA with core and human signal peptide peptidase in yeast did not produce phosphorylated NLPs and led to a decreased accumulation of nonenveloped particles. Mutation S116A restored the core protein content. These results suggest that PKA phosphorylation can modulate HCV core levels in infected cells.
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DaFonseca, Sandrina, Armand Blommaert, Pascale Coric, Saw See Hong, Serge Bouaziz, and Pierre Boulanger. "The 3-O-(3’,3’-dimethylsuccinyl) derivative of betulinic acid (DSB) inhibits the assembly of virus-like particles in HIV-1 Gag precursor-expressing cells." Antiviral Therapy 12, no. 8 (November 2007): 1185–204. http://dx.doi.org/10.1177/135965350701200807.
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Background The 3- O-(3’,3’-dimethylsuccinyl) derivative of betulinic acid (DSB) blocks HIV-1 maturation by interfering with viral protease (PR) at the capsid (CA)-SP1 cleavage site, a crucial region in HIV-1 morphogenesis. Methods We analysed the effect of DSB on the assembly of HIV-1 Gag precursor (Pr55GagHIV) into membrane-enveloped virus-like particles (VLP) in baculovirus-infected cells expressing Pr55GagHIV, in a cellular context devoid of viral PR. Results DSB showed a dose-dependent negative effect on VLP assembly, with an IC50∼10 μM. The DSB inhibitory effect was p6-independent and was also observed for intracellular assembly of non-N-myristoylated Gag core-like particles. HIV-1 VLP assembled in the presence of DSB exhibited a lower stability of their inner cores upon membrane delipidation compared with control VLP, suggesting weaker Gag-Gag interactions. DSB also inhibited the assembly of simian immunodeficiency virus SIVmac251 VLP, although with a twofold lower efficacy (IC50∼20 μM). No detectable inhibitory activity was observed for murine leukaemia virus (MLV) VLP; however, fusion of the SP1-NC-p6 domains from HIV-1 to the matrix (MA)-CA domains from MLV conferred DSB sensitivity to the chimaeric Gag precursor Pr72GagMLV–HIV (IC50=30 μM). This observation suggested that the main DSB target on Pr55Gag was the SP1 domain, but the higher degree of DSB resistance for Pr72GagMLV–HIV compared with Pr55GagHIV implied that other upstream Gag region(s) might contribute to DSB reactivity. Conclusions Sequence alignment and three-dimensional modelling by homology of the CA-SP1-NC junction in HIV-1, SIVmac251 and Pr72GagMLV–HIV suggested that a higher hydrophilic character of the CA region immediately upstream to the HIV-1 CA-SP1 junction, as occurred in Pr72GagMLV–HIV, correlated with a lower DSB sensitivity.
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de Rocquigny, Hugues, Virgile Rat, Florentin Pastor, Jean Luc Darlix, Christophe Hourioux, and Philippe Roingeard. "Phosphorylation of the Arginine-Rich C-Terminal Domains of the Hepatitis B Virus (HBV) Core Protein as a Fine Regulator of the Interaction between HBc and Nucleic Acid." Viruses 12, no. 7 (July 8, 2020): 738. http://dx.doi.org/10.3390/v12070738.
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The morphogenesis of Hepatitis B Virus (HBV) viral particles is nucleated by the oligomerization of HBc protein molecules, resulting in the formation of an icosahedral capsid shell containing the replication-competent nucleoprotein complex made of the viral polymerase and the pre-genomic RNA (pgRNA). HBc is a phospho-protein containing two distinct domains acting together throughout the viral replication cycle. The N-terminal domain, (residues 1–140), shown to self-assemble, is linked by a short flexible domain to the basic C-terminal domain (residues 150–183) that interacts with nucleic acids (NAs). In addition, the C-terminal domain contains a series of phospho-acceptor residues that undergo partial phosphorylation and de-phosphorylation during virus replication. This highly dynamic process governs the homeostatic charge that is essential for capsid stability, pgRNA packaging and to expose the C-terminal domain at the surface of the particles for cell trafficking. In this review, we discuss the roles of the N-terminal and C-terminal domains of HBc protein during HBV morphogenesis, focusing on how the C-terminal domain phosphorylation dynamics regulate its interaction with nucleic acids throughout the assembly and maturation of HBV particles.
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Fu, William, Que Dang, Kunio Nagashima, Eric O. Freed, Vinay K. Pathak, and Wei-Shau Hu. "Effects of Gag Mutation and Processing on Retroviral Dimeric RNA Maturation." Journal of Virology 80, no. 3 (February 1, 2006): 1242–49. http://dx.doi.org/10.1128/jvi.80.3.1242-1249.2006.
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ABSTRACT After their release from host cells, most retroviral particles undergo a maturation process, which includes viral protein cleavage, core condensation, and increased stability of the viral RNA dimer. Inactivating the viral protease prevents protein cleavage; the resulting virions lack condensed cores and contain fragile RNA dimers. Therefore, protein cleavage is linked to virion morphological change and increased stability of the RNA dimer. However, it is unclear whether protein cleavage is sufficient for mediating virus RNA maturation. We have observed a novel phenotype in a murine leukemia virus capsid mutant, which has normal virion production, viral protein cleavage, and RNA packaging. However, this mutant also has immature virion morphology and contains a fragile RNA dimer, which is reminiscent of protease-deficient mutants. To our knowledge, this mutant provides the first evidence that Gag cleavage alone is not sufficient to promote RNA dimer maturation. To extend our study further, we examined a well-defined human immunodeficiency virus type 1 (HIV-1) Gag mutant that lacks a functional PTAP motif and produces immature virions without major defects in viral protein cleavage. We found that the viral RNA dimer in the PTAP mutant is more fragile and unstable compared with those from wild-type HIV-1. Based on the results of experiments using two different Gag mutants from two distinct retroviruses, we conclude that Gag cleavage is not sufficient for promoting RNA dimer maturation, and we propose that there is a link between the maturation of virion morphology and the viral RNA dimer.
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Chua, Pong Kian, Fan-Mei Tang, Jyuan-Yuan Huang, Ching-Shu Suen, and Chiaho Shih. "Testing the Balanced Electrostatic Interaction Hypothesis of Hepatitis B Virus DNA Synthesis by Using an In Vivo Charge Rebalance Approach." Journal of Virology 84, no. 5 (December 16, 2009): 2340–51. http://dx.doi.org/10.1128/jvi.01666-09.
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ABSTRACT Previously, a charge balance hypothesis was proposed to explain hepatitis B virus (HBV) capsid stability, assembly, RNA encapsidation, and DNA replication. This hypothesis emphasized the importance of a balanced electrostatic interaction between the positive charge from the arginine-rich domain (ARD) of the core protein (HBc) and the negative charge from the encapsidated nucleic acid. It remains unclear if any of the negative charge involved in this electrostatic interaction could come from the HBc protein per se, in addition to the encapsidated nucleic acid. HBc ARD IV mutant 173GG and ARD II mutant 173RR/R157A/R158A are arginine deficient and replication defective. Not surprisingly, the replication defect of ARD IV mutant 173GG can be rescued by restoring positively charged amino acids at the adjacent positions 174 and 175. However, most interestingly, it can be at least partially rescued by reducing negatively charged residues in the assembly domain, such as by glutamic acid-to-alanine (E-to-A) substitutions at position 46 or 117 and to a much lesser extent at position 113. Similar results were obtained for ARD II mutant 173RR/R157A/R158A. These amino acids are located on the inner surfaces of HBc icosahedral particles, and their acidic side chains point toward the capsid interior. For HBV DNA synthesis, the relative amount of positive versus negative charge in the electrostatic interactions is more important than the absolute amount of positive or negative charge. These results support the concept that balanced electrostatic interaction is important during the viral life cycle.
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Liu, Hui, Junjun Cheng, Usha Viswanathan, Jinhong Chang, Fengmin Lu, and Ju-Tao Guo. "Amino acid residues at core protein dimer-dimer interface modulate multiple steps of hepatitis B virus replication and HBeAg biogenesis." PLOS Pathogens 17, no. 11 (November 9, 2021): e1010057. http://dx.doi.org/10.1371/journal.ppat.1010057.
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The core protein (Cp) of hepatitis B virus (HBV) assembles pregenomic RNA (pgRNA) and viral DNA polymerase to form nucleocapsids where the reverse transcriptional viral DNA replication takes place. Core protein allosteric modulators (CpAMs) inhibit HBV replication by binding to a hydrophobic “HAP” pocket at Cp dimer-dimer interfaces to misdirect the assembly of Cp dimers into aberrant or morphologically “normal” capsids devoid of pgRNA. We report herein that a panel of CpAM-resistant Cp with single amino acid substitution of residues at the dimer-dimer interface not only disrupted pgRNA packaging, but also compromised nucleocapsid envelopment, virion infectivity and covalently closed circular (ccc) DNA biosynthesis. Interestingly, these mutations also significantly reduced the secretion of HBeAg. Biochemical analysis revealed that the CpAM-resistant mutations in the context of precore protein (p25) did not affect the levels of p22 produced by signal peptidase removal of N-terminal 19 amino acid residues, but significantly reduced p17, which is produced by furin cleavage of C-terminal arginine-rich domain of p22 and secreted as HBeAg. Interestingly, p22 existed as both unphosphorylated and phosphorylated forms. While the unphosphorylated p22 is in the membranous secretary organelles and the precursor of HBeAg, p22 in the cytosol and nuclei is hyperphosphorylated at the C-terminal arginine-rich domain and interacts with Cp to disrupt capsid assembly and viral DNA replication. The results thus indicate that in addition to nucleocapsid assembly, interaction of Cp at dimer-dimer interface also plays important roles in the production and infectivity of progeny virions through modulation of nucleocapsid envelopment and uncoating. Similar interaction at reduced p17 dimer-dimer interface appears to be important for its metabolic stability and sensitivity to CpAM suppression of HBeAg secretion.
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Shen, Qi, Chunxiang Wu, Christian Freniere, Therese N. Tripler, and Yong Xiong. "Nuclear Import of HIV-1." Viruses 13, no. 11 (November 8, 2021): 2242. http://dx.doi.org/10.3390/v13112242.
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The delivery of the HIV-1 genome into the nucleus is an indispensable step in retroviral infection of non-dividing cells, but the mechanism of HIV-1 nuclear import has been a longstanding debate due to controversial experimental evidence. It was commonly believed that the HIV-1 capsid would need to disassemble (uncoat) in the cytosol before nuclear import because the capsid is larger than the central channel of nuclear pore complexes (NPCs); however, increasing evidence demonstrates that intact, or nearly intact, HIV-1 capsid passes through the NPC to enter the nucleus. With the protection of the capsid, the HIV-1 core completes reverse transcription in the nucleus and is translocated to the integration site. Uncoating occurs while, or after, the viral genome is released near the integration site. These independent discoveries reveal a compelling new paradigm of this important step of the HIV-1 life cycle. In this review, we summarize the recent studies related to HIV-1 nuclear import, highlighting the spatial–temporal relationship between the nuclear entry of the virus core, reverse transcription, and capsid uncoating.
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Luban, Jeremy. "TRIM5 and the Regulation of HIV-1 Infectivity." Molecular Biology International 2012 (May 30, 2012): 1–6. http://dx.doi.org/10.1155/2012/426840.
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The past ten years have seen an explosion of information concerning host restriction factors that inhibit the replication of HIV-1 and other retroviruses. Among these factors is TRIM5, an innate immune signaling molecule that recognizes the capsid lattice as soon as the retrovirion core is released into the cytoplasm of otherwise susceptible target cells. Recognition of the capsid lattice has several consequences that include multimerization of TRIM5 into a complementary lattice, premature uncoating of the virion core, and activation of TRIM5 E3 ubiquitin ligase activity. Unattached, K63-linked ubiquitin chains are generated that activate the TAK1 kinase complex and downstream inflammatory mediators. Polymorphisms in the capsid recognition domain of TRIM5 explain the observed species-specific differences among orthologues and the relatively weak anti-HIV-1 activity of human TRIM5. Better understanding of the complex interaction between TRIM5 and the retrovirus capsid lattice may someday lead to exploitation of this interaction for the development of potent HIV-1 inhibitors.
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Buffone, Cindy, Bianca Schulte, Silvana Opp, and Felipe Diaz-Griffero. "Contribution of MxB Oligomerization to HIV-1 Capsid Binding and Restriction." Journal of Virology 89, no. 6 (January 7, 2015): 3285–94. http://dx.doi.org/10.1128/jvi.03730-14.
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ABSTRACTThe alpha interferon (IFN-α)-inducible restriction factor myxovirus B (MxB) blocks HIV-1 infection after reverse transcription but prior to integration. MxB binds to the HIV-1 core, which is composed of capsid protein, and this interaction leads to inhibition of the uncoating process of HIV-1. Previous studies suggested that HIV-1 restriction by MxB requires binding to capsid. This work tests the hypothesis that MxB oligomerization is important for the ability of MxB to bind to the HIV-1 core. For this purpose, we modeled the structure of MxB using the published tertiary structure of MxA. The modeled structure of MxB guided our mutagenic studies and led to the discovery of several MxB variants that lose the capacity to oligomerize. In agreement with our hypothesis, MxB variants that lost the oligomerization capacity also lost the ability to bind to the HIV-1 core. MxB variants deficient for oligomerization were not able to block HIV-1 infection. Overall, our work showed that oligomerization is required for the ability of MxB to bind to the HIV-1 core and block HIV-1 infection.IMPORTANCEMxB is a novel restriction factor that blocks infection of HIV-1. MxB is inducible by IFN-α, particularly in T cells. The current work studies the oligomerization determinants of MxB and carefully explores the contribution of oligomerization to capsid binding and restriction. This work takes advantage of the current structure of MxA and models the structure of MxB, which is used to guide structure-function studies. This work leads to the conclusion that MxB oligomerization is important for HIV-1 capsid binding and restriction.
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Forshey, Brett M., Jiong Shi, and Christopher Aiken. "Structural Requirements for Recognition of the Human Immunodeficiency Virus Type 1 Core during Host Restriction in Owl Monkey Cells." Journal of Virology 79, no. 2 (January 15, 2005): 869–75. http://dx.doi.org/10.1128/jvi.79.2.869-875.2005.
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ABSTRACT Human immunodeficiency virus type 1 (HIV-1) infection of simian cells is restricted at an early postentry step by host factors whose mechanism of action is unclear. These factors target the viral capsid protein (CA) and attenuate reverse transcription, suggesting that they bind to the HIV-1 core and interfere with its uncoating. To identify the relevant binding determinants in the capsid, we tested the capacity of viruses containing Gag cleavage site mutations and amino acid substitutions in CA to inhibit restriction of a wild type HIV-1 reporter virus in owl monkey cells. The results demonstrated that a stable, polymeric capsid and a correctly folded amino-terminal CA subunit interface are essential for saturation of host restriction in target cells by HIV-1 cores. We conclude that the owl monkey cellular restriction machinery recognizes a polymeric array of CA molecules, most likely via direct engagement of the HIV-1 capsid in target cells prior to uncoating.
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Skorupka, Katarzyna A., Marcin D. Roganowicz, Devin E. Christensen, Yueping Wan, Owen Pornillos, and Barbie K. Ganser-Pornillos. "Hierarchical assembly governs TRIM5α recognition of HIV-1 and retroviral capsids." Science Advances 5, no. 11 (November 2019): eaaw3631. http://dx.doi.org/10.1126/sciadv.aaw3631.
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TRIM5α is a restriction factor that senses incoming retrovirus cores through an unprecedented mechanism of nonself recognition. TRIM5α assembles a hexagonal lattice that avidly binds the capsid shell, which surrounds and protects the virus core. The extent to which the TRIM lattice can cover the capsid and how TRIM5α directly contacts the capsid surface have not been established. Here, we apply cryo–electron tomography and subtomogram averaging to determine structures of TRIM5α bound to recombinant HIV-1 capsid assemblies. Our data support a mechanism of hierarchical assembly, in which a limited number of basal interaction modes are successively organized in increasingly higher-order structures that culminate in a TRIM5α cage surrounding a retroviral capsid. We further propose that cage formation explains the mechanism of restriction and provides the structural context that links capsid recognition to ubiquitin-dependent processes that disable the retrovirus.
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AlBurtamani, Nawal, Alwin Paul, and Ariberto Fassati. "The Role of Capsid in the Early Steps of HIV-1 Infection: New Insights into the Core of the Matter." Viruses 13, no. 6 (June 17, 2021): 1161. http://dx.doi.org/10.3390/v13061161.
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In recent years, major advances in research and experimental approaches have significantly increased our knowledge on the role of the HIV-1 capsid in the virus life cycle, from reverse transcription to integration and gene expression. This makes the capsid protein a good pharmacological target to inhibit HIV-1 replication. This review covers our current understanding of the role of the viral capsid in the HIV-1 life cycle and its interaction with different host factors that enable reverse transcription, trafficking towards the nucleus, nuclear import and integration into host chromosomes. It also describes different promising small molecules, some of them in clinical trials, as potential targets for HIV-1 therapy.
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Dick, Robert, Donna Mallery, Volker Vogt, and Leo James. "IP6 Regulation of HIV Capsid Assembly, Stability, and Uncoating." Viruses 10, no. 11 (November 15, 2018): 640. http://dx.doi.org/10.3390/v10110640.
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The mechanisms that drive formation of the HIV capsid, first as an immature particle and then as a mature protein shell, remain incompletely understood. Recent discoveries of positively-charged rings in the immature and mature protein hexamer subunits that comprise them and their binding to the cellular metabolite inositol hexakisphosphate (IP6) have stimulated exciting new hypotheses. In this paper, we discuss how data from multiple structural and biochemical approaches are revealing potential roles for IP6 in the HIV-1 replication cycle from assembly to uncoating.
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Li, Yuan, Alak Kanti Kar, and Joseph Sodroski. "Target Cell Type-Dependent Modulation of Human Immunodeficiency Virus Type 1 Capsid Disassembly by Cyclophilin A." Journal of Virology 83, no. 21 (August 5, 2009): 10951–62. http://dx.doi.org/10.1128/jvi.00682-09.
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ABSTRACT The binding of cyclophilin A (CypA) to the human immunodeficiency virus type 1 (HIV-1) capsid protein (CA protein) is required soon after virus entry into natural target cells. In Jurkat T lymphocytes, disrupting CypA-CA interaction either by cyclosporine (Cs) treatment or by alteration (e.g., P90A) of the CA inhibits HIV-1 infection. In HeLa cells, however, treatment with Cs or Cs analogues minimally inhibits the early phase of HIV-1 infection but selects for a Cs-dependent virus with a change (A92E) in CA. To understand these phenomena, we examined the effects of the P90A and A92E changes in the HIV-1 CA protein on the stability of capsid complexes assembled in vitro and on capsid disassembly in the cytosol of virus-exposed target cells. The A92E change impaired CA-CA interactions in vitro and decreased the amount of particulate capsids in the cytosol of HeLa target cells. Reducing the binding of CypA to the A92E mutant capsid, either by Cs treatment or by an additional P90A change in the CA protein, increased the amount of particulate capsids and viral infectivity in HeLa cells. In contrast, reduction of the binding of CypA to HIV-1 capsids in Jurkat T lymphocytes resulted in a decrease in the amount of particulate capsids and infectivity. Thus, depending on the capsid and the target cell, CypA-CA binding either stabilized or destabilized the capsid, indicating that CypA modulates HIV-1 capsid disassembly. In both cell types examined, decreased stability of the capsid was associated with a decrease in the efficiency of HIV-1 infection.
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Abdurahman, Samir, Ákos Végvári, Masoud Youssefi, Michael Levi, Stefan Höglund, Elin Andersson, Peter Horal, Bo Svennerholm, Jan Balzarini, and Anders Vahlne. "Activity of the Small Modified Amino Acid α-Hydroxy Glycineamide on In Vitro and In Vivo Human Immunodeficiency Virus Type 1 Capsid Assembly and Infectivity." Antimicrobial Agents and Chemotherapy 52, no. 10 (July 21, 2008): 3737–44. http://dx.doi.org/10.1128/aac.00265-08.
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ABSTRACT Upon maturation of the human immunodeficiency virus type 1 (HIV-1) virion, proteolytic cleavage of the Gag precursor protein by the viral protease is followed by morphological changes of the capsid protein p24, which will ultimately transform the virus core from an immature spherical to a mature conical structure. Virion infectivity is critically dependent on the optimal semistability of the capsid cone structure. We have reported earlier that glycineamide (G-NH2), when added to the culture medium of infected cells, inhibits HIV-1 replication and that HIV-1 particles with aberrant core structures were formed. Here we show that it is not G-NH2 itself but a metabolite thereof, α-hydroxy-glycineamide (α-HGA), that is responsible for the antiviral activity. We show that α-HGA inhibits the replication of clinical HIV-1 isolates with acquired resistance to reverse transcriptase and protease inhibitors but has no effect on the replication of any of 10 different RNA and DNA viruses. α-HGA affected the ability of the HIV-1 capsid protein to assemble into tubular or core structures in vitro and in vivo, probably by binding to the hinge region between the N- and C-terminal domains of the HIV-1 capsid protein as indicated by matrix-assisted laser desorption ionization-mass spectrometry results. As an antiviral compound, α-HGA has an unusually simple structure, a pronounced antiviral specificity, and a novel mechanism of antiviral action. As such, it might prove to be a lead compound for a new class of anti-HIV substances.
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Schulte, Bianca, Cindy Buffone, Silvana Opp, Francesca Di Nunzio, Daniel Augusto De Souza Aranha Vieira, Alberto Brandariz-Nuñez, and Felipe Diaz-Griffero. "Restriction of HIV-1 Requires the N-Terminal Region of MxB as a Capsid-Binding Motif but Not as a Nuclear Localization Signal." Journal of Virology 89, no. 16 (June 10, 2015): 8599–610. http://dx.doi.org/10.1128/jvi.00753-15.
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ABSTRACTThe interferon alpha (IFN-α)-inducible restriction factor MxB blocks HIV-1 infection after reverse transcription but prior to integration. Fate-of-capsid experiments have correlated the ability of MxB to block HIV-1 infection with stabilization of viral cores during infection. We previously demonstrated that HIV-1 restriction by MxB requires capsid binding and oligomerization. Deletion and gain-of-function experiments have mapped the HIV-1 restriction ability of MxB to its N-terminal 25 amino acids. This report reveals that the N-terminal 25 amino acids of MxB exhibit two separate functions: (i) the ability of MxB to bind to HIV-1 capsid and (ii) the nuclear localization signal of MxB, which is important for the ability of MxB to shuttle into the nucleus. To understand whether MxB restriction of HIV-1 requires capsid binding and/or nuclear localization, we genetically separated these two functions and evaluated their contributions to restriction. Our experiments demonstrated that the11RRR13motif is important for the ability of MxB to bind capsid and to restrict HIV-1 infection. These experiments suggested that capsid binding is necessary for the ability of MxB to block HIV-1 infection. Separately from the capsid binding function of MxB, we found that residues20KY21regulate the ability of the N-terminal 25 amino acids of MxB to function as a nuclear localization signal; however, the ability of the N-terminal 25 amino acids to function as a nuclear localization signal was not required for restriction.IMPORTANCEMxB/Mx2 blocks HIV-1 infection in cells from the immune system. MxB blocks infection by preventing the uncoating process of HIV-1. The ability of MxB to block HIV-1 infection requires that MxB binds to the HIV-1 core by using its N-terminal domain. The present study shows that MxB uses residues11RRR13to bind to the HIV-1 core during infection and that these residues are required for the ability of MxB to block HIV-1 infection. We also found that residues20KY21constitute a nuclear localization signal that is not required for the ability of MxB to block HIV-1 infection.
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Gruenke, Paige R., Rachna Aneja, Sarah Welbourn, Obiaara B. Ukah, Stefan G. Sarafianos, Donald H. Burke, and Margaret J. Lange. "Selection and identification of an RNA aptamer that specifically binds the HIV-1 capsid lattice and inhibits viral replication." Nucleic Acids Research 50, no. 3 (January 8, 2022): 1701–17. http://dx.doi.org/10.1093/nar/gkab1293.
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Abstract The HIV-1 capsid core participates in several replication processes. The mature capsid core is a lattice composed of capsid (CA) monomers thought to assemble first into CA dimers, then into ∼250 CA hexamers and 12 CA pentamers. CA assembly requires conformational flexibility of each unit, resulting in the presence of unique, solvent-accessible surfaces. Significant advances have improved our understanding of the roles of the capsid core in replication; however, the contributions of individual CA assembly forms remain unclear and there are limited tools available to evaluate these forms in vivo. Here, we have selected aptamers that bind CA lattice tubes. We describe aptamer CA15-2, which selectively binds CA lattice, but not CA monomer or CA hexamer, suggesting that it targets an interface present and accessible only on CA lattice. CA15-2 does not compete with PF74 for binding, indicating that it likely binds a non-overlapping site. Furthermore, CA15-2 inhibits HIV-1 replication when expressed in virus producer cells, but not target cells, suggesting that it binds a biologically-relevant site during virus production that is either not accessible during post-entry replication steps or is accessible but unaltered by aptamer binding. Importantly, CA15-2 represents the first aptamer that specifically recognizes the HIV-1 CA lattice.
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Ingram, Zachary, Hannah Matheney, Emma Wise, Courtney Weatherford, and Amy E. Hulme. "Overlap Intensity: An ImageJ Macro for Analyzing the HIV-1 In Situ Uncoating Assay." Viruses 13, no. 8 (August 13, 2021): 1604. http://dx.doi.org/10.3390/v13081604.
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Capsid uncoating is at the crossroads of early steps in HIV-1 replication. In recent years, the development of novel assays has expanded how HIV-1 uncoating can be studied. In the in situ uncoating assay, dual fluorescently labelled virus allows for the identification of fused viral cores. Antibody staining then detects the amount of capsid associated with each viral core at different times post-infection. Following fixed cell imaging, manual counting can be used to assess the fusion state and capsid signal for each viral core, but this method can introduce bias with increased time of analysis. To address these limitations, we developed the Overlap Intensity macro in ImageJ. This macro automates the detection of viral cores and quantification of overlapping fusion and capsid signals. We demonstrated the high accuracy of the macro by comparing core detection to manual methods. Analysis of an in situ uncoating assay further verified the macro by detecting progressive uncoating as expected. Therefore, this macro improves the accessibility of the in situ uncoating assay by replacing time-consuming manual methods or the need for expensive data analysis software. Beyond the described assay, the Overlap Intensity macro includes adjustable settings for use in other methods requiring quantification of overlapping fluorescent signals.
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Mattei, Simone, Annica Flemming, Maria Anders-Össwein, Hans-Georg Kräusslich, John A. G. Briggs, and Barbara Müller. "RNA and Nucleocapsid Are Dispensable for Mature HIV-1 Capsid Assembly." Journal of Virology 89, no. 19 (July 15, 2015): 9739–47. http://dx.doi.org/10.1128/jvi.00750-15.
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ABSTRACTHuman immunodeficiency virus type 1 (HIV-1) is released from infected cells in an immature, noninfectious form in which the structural polyprotein Gag is arranged in a hexameric lattice, forming an incomplete spherical shell. Maturation to the infectious form is mediated by the viral protease, which cleaves Gag at five sites, releasing the CA (capsid) protein, which forms a conical capsid encasing the condensed RNA genome. The pathway of this structural rearrangement is currently not understood, and it is unclear how cone assembly is initiated. RNA represents an integral structural component of retroviruses, and the viral nucleoprotein core has previously been proposed to nucleate mature capsid assembly. We addressed this hypothesis by replacing the RNA-binding NC (nucleocapsid) domain of HIV-1 Gag and the adjacent spacer peptide 2 (SP2) by a leucine zipper (LZ) protein-protein interaction domain [Gag(LZ)] in the viral context. We found that Gag(LZ)-carrying virus [HIV(LZ)] was efficiently released and viral polyproteins were proteolytically processed, though with reduced efficiency. Cryo-electron tomography revealed that the particles lacked a condensed nucleoprotein and contained an increased proportion of aberrant core morphologies caused either by the absence of RNA or by altered Gag processing. Nevertheless, a significant proportion of HIV(LZ) particles contained mature capsids with the wild-type morphology. These results clearly demonstrate that the nucleoprotein complex is dispensable as a nucleator for mature HIV-1 capsid assembly in the viral context.IMPORTANCEFormation of a closed conical capsid encasing the viral RNA genome is essential for HIV-1 infectivity. It is currently unclear what viral components initiate and regulate the formation of the capsid during virus morphogenesis, but it has been proposed that the ribonucleoprotein complex plays a role. To test this, we prepared virus-like particles lacking the viral nucleocapsid protein and RNA and analyzed their three-dimensional structure by cryo-electron tomography. While most virions displayed an abnormal morphology under these conditions, some particles showed a normal mature morphology with closed conical capsids. These data demonstrate that the presence of RNA and the nucleocapsid protein is not required for the formation of a mature, cone-shaped HIV-1 capsid.
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Rossi, Eric, Megan E. Meuser, Camille J. Cunanan, and Simon Cocklin. "Structure, Function, and Interactions of the HIV-1 Capsid Protein." Life 11, no. 2 (January 29, 2021): 100. http://dx.doi.org/10.3390/life11020100.
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The capsid (CA) protein of the human immunodeficiency virus type 1 (HIV-1) is an essential structural component of a virion and facilitates many crucial life cycle steps through interactions with host cell factors. Capsid shields the reverse transcription complex from restriction factors while it enables trafficking to the nucleus by hijacking various adaptor proteins, such as FEZ1 and BICD2. In addition, the capsid facilitates the import and localization of the viral complex in the nucleus through interaction with NUP153, NUP358, TNPO3, and CPSF-6. In the later stages of the HIV-1 life cycle, CA plays an essential role in the maturation step as a constituent of the Gag polyprotein. In the final phase of maturation, Gag is cleaved, and CA is released, allowing for the assembly of CA into a fullerene cone, known as the capsid core. The fullerene cone consists of ~250 CA hexamers and 12 CA pentamers and encloses the viral genome and other essential viral proteins for the next round of infection. As research continues to elucidate the role of CA in the HIV-1 life cycle and the importance of the capsid protein becomes more apparent, CA displays potential as a therapeutic target for the development of HIV-1 inhibitors.
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Wiegers, Klaus, Gabriel Rutter, Hubert Kottler, Uwe Tessmer, Heinz Hohenberg, and Hans-Georg Kräusslich. "Sequential Steps in Human Immunodeficiency Virus Particle Maturation Revealed by Alterations of Individual Gag Polyprotein Cleavage Sites." Journal of Virology 72, no. 4 (April 1, 1998): 2846–54. http://dx.doi.org/10.1128/jvi.72.4.2846-2854.1998.
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ABSTRACT Retroviruses are produced as immature particles containing structural polyproteins, which are subsequently cleaved by the viral proteinase (PR). Extracellular maturation leads to condensation of the spherical core to a capsid shell formed by the capsid (CA) protein, which encases the genomic RNA complexed with nucleocapsid (NC) proteins. CA and NC are separated by a short spacer peptide (spacer peptide 1 [SP1]) on the human immunodeficiency virus type 1 (HIV-1) Gag polyprotein and released by sequential PR-mediated cleavages. To assess the role of individual cleavages in maturation, we constructed point mutations abolishing cleavage at these sites, either alone or in combination. When all three sites between CA and NC were mutated, immature particles containing stable CA-NC were observed, with no apparent effect on other cleavages. Delayed maturation with irregular morphology of the ribonucleoprotein core was observed when cleavage of SP1 from NC was prevented. Blocking the release of SP1 from CA, on the other hand, yielded normal condensation of the ribonucleoprotein core but prevented capsid condensation. A thin, electron-dense layer near the viral membrane was observed in this case, and mutant capsids were significantly less stable against detergent treatment than wild-type HIV-1. We suggest that HIV maturation is a sequential process controlled by the rate of cleavage at individual sites. Initial rapid cleavage at the C terminus of SP1 releases the RNA-binding NC protein and leads to condensation of the ribonucleoprotein core. Subsequently, CA is separated from the membrane by cleavage between the matrix protein and CA, and late release of SP1 from CA is required for capsid condensation.
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Gres, Anna T., Karen A. Kirby, Vineet N. KewalRamani, John J. Tanner, Owen Pornillos, and Stefan G. Sarafianos. "X-ray crystal structures of native HIV-1 capsid protein reveal conformational variability." Science 349, no. 6243 (June 4, 2015): 99–103. http://dx.doi.org/10.1126/science.aaa5936.
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The detailed molecular interactions between native HIV-1 capsid protein (CA) hexamers that shield the viral genome and proteins have been elusive. We report crystal structures describing interactions between CA monomers related by sixfold symmetry within hexamers (intrahexamer) and threefold and twofold symmetry between neighboring hexamers (interhexamer). The structures describe how CA builds hexagonal lattices, the foundation of mature capsids. Lattice structure depends on an adaptable hydration layer modulating interactions among CA molecules. Disruption of this layer alters interhexamer interfaces, highlighting an inherent structural variability. A CA-targeting antiviral affects capsid stability by binding across CA molecules and subtly altering interhexamer interfaces remote to the ligand-binding site. Inherent structural plasticity, hydration layer rearrangement, and effector binding affect capsid stability and have functional implications for the retroviral life cycle.
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Ylinen, Laura M. J., Torsten Schaller, Amanda Price, Adam J. Fletcher, Mahdad Noursadeghi, Leo C. James, and Greg J. Towers. "Cyclophilin A Levels Dictate Infection Efficiency of Human Immunodeficiency Virus Type 1 Capsid Escape Mutants A92E and G94D." Journal of Virology 83, no. 4 (December 10, 2008): 2044–47. http://dx.doi.org/10.1128/jvi.01876-08.
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ABSTRACT Cyclophilin A (CypA) is an important human immunodeficiency virus type 1 (HIV-1) cofactor in human cells. HIV-1 A92E and G94D capsid escape mutants arise during CypA inhibition and in certain cell lines are dependent on CypA inhibition. Here we show that dependence on CypA inhibition is due to high CypA levels. Restricted HIV-1 is stable, and remarkably, restriction is augmented by arresting cell division. Nuclear entry is not inhibited. We propose that high CypA levels and capsid mutations combine to disturb uncoating, leading to poor infectivity, particularly in arrested cells. Our data suggest a role for CypA in uncoating the core of HIV-1 to facilitate integration.
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Yu, Alvin, Elizabeth M. Y. Lee, Jaehyeok Jin, and Gregory A. Voth. "Atomic-scale characterization of mature HIV-1 capsid stabilization by inositol hexakisphosphate (IP6)." Science Advances 6, no. 38 (September 2020): eabc6465. http://dx.doi.org/10.1126/sciadv.abc6465.
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Inositol hexakisphosphates (IP6) are cellular cofactors that promote the assembly of mature capsids of HIV. These negatively charged molecules coordinate an electropositive ring of arginines at the center of pores distributed throughout the capsid surface. Kinetic studies indicate that the binding of IP6 increases the stable lifetimes of the capsid by several orders of magnitude from minutes to hours. Using all-atom molecular dynamics simulations, we uncover the mechanisms that underlie the unusually high stability of mature capsids in complex with IP6. We find that capsid hexamers and pentamers have differential binding modes for IP6. Ligand density calculations show three sites of interaction with IP6 including at a known capsid inhibitor binding pocket. Free energy calculations demonstrate that IP6 preferentially stabilizes pentamers over hexamers to enhance fullerene modes of assembly. These results elucidate the molecular role of IP6 in stabilizing and assembling the retroviral capsid.
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Gummersheimer, Stephanie L., Anthony J. Snyder, and Pranav Danthi. "Control of Capsid Transformations during Reovirus Entry." Viruses 13, no. 2 (January 21, 2021): 153. http://dx.doi.org/10.3390/v13020153.
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Mammalian orthoreovirus (reovirus), a dsRNA virus with a multilayered capsid, serves as a model system for studying the entry of similar viruses. The outermost layer of this capsid undergoes processing to generate a metastable intermediate. The metastable particle undergoes further remodeling to generate an entry-capable form that delivers the genome-containing inner capsid, or core, into the cytoplasm. In this review, we highlight capsid proteins and the intricacies of their interactions that control the stability of the capsid and consequently impact capsid structural changes that are prerequisites for entry. We also discuss a novel proviral role of host membranes in promoting capsid conformational transitions. Current knowledge gaps in the field that are ripe for future investigation are also outlined.
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Misselwitz, Rolf, Gert Hausdorf, Karin Welfle, Wolfgang E. Höhne, and Heinz Welfle. "Conformation and stability of recombinant HIV-1 capsid protein p24 (rp24)." Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology 1250, no. 1 (July 1995): 9–18. http://dx.doi.org/10.1016/0167-4838(95)00041-r.
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Li, Chenglei, Ryan C. Burdick, Kunio Nagashima, Wei-Shau Hu, and Vinay K. Pathak. "HIV-1 cores retain their integrity until minutes before uncoating in the nucleus." Proceedings of the National Academy of Sciences 118, no. 10 (March 1, 2021): e2019467118. http://dx.doi.org/10.1073/pnas.2019467118.
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We recently reported that HIV-1 cores that retained >94% of their capsid (CA) protein entered the nucleus and disassembled (uncoated) near their integration site <1.5 h before integration. However, whether the nuclear capsids lost their integrity by rupturing or a small loss of CA before capsid disassembly was unclear. Here, we utilized a previously reported vector in which green fluorescent protein is inserted in HIV-1 Gag (iGFP); proteolytic processing efficiently releases GFP, some of which remains trapped inside capsids and serves as a fluid phase content marker that is released when the capsids lose their integrity. We found that nuclear capsids retained their integrity until shortly before integration and lost their GFP content marker ∼1 to 3 min before loss of capsid-associated mRuby-tagged cleavage and polyadenylation specificity factor 6 (mRuby-CPSF6). In contrast, loss of GFP fused to CA and mRuby-CPSF6 occurred simultaneously, indicating that viral cores retain their integrity until just minutes before uncoating. Our results indicate that HIV-1 evolved to retain its capsid integrity and maintain a separation between macromolecules in the viral core and the nuclear environment until uncoating occurs just before integration. These observations imply that intact HIV-1 capsids are imported through nuclear pores; that reverse transcription occurs in an intact capsid; and that interactions between the preintegration complex and LEDGF/p75, and possibly other host factors that facilitate integration, must occur during the short time period between loss of capsid integrity and integration.
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Miles, Penny, Peter Cassidy, Lynn Donlon, Orr Yarkoni, and Daniel Frankel. "In vitro assembly of a viral envelope." Soft Matter 11, no. 39 (2015): 7722–27. http://dx.doi.org/10.1039/c5sm01695a.
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Swan, Christina H., Udayan Chatterji, Philippe Gallay, and Bruce E. Torbett. "A Cyclophilin A-Independent Capsid Motif Renders HIV-1 Derived Vectors More Efficient at Transducing Human Cells." Blood 106, no. 11 (November 16, 2005): 5531. http://dx.doi.org/10.1182/blood.v106.11.5531.5531.
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Abstract We recently identified naturally occurring HIV-1 capsid (CA) motifs, which evade both cyclophilin A (CypA)-dependence in human cells and TRIM-5α-CypA (TRIM-Cyp) restriction in owl monkey kidney (OMK) cells (Chatterji, et al. JBC, In press). These HIV-1 capsid motifs contained either one (G89V) or four (V86P/H87Q/I91V/M96I) amino acid substitutions within the CypA binding site, but only the four amino acid mutant was able to bind CypA, yet does not require CypA incorporation to infect human cells. OMK cells are naturally resistant to HIV-1 infection due to TRIM-Cyp, a negative host factor, which efficiently targets incoming wild type HIV-1 capsid and thereby prevents the proper uncoating of the CA core. However, addition of cyclosporine A, which blocks the interaction of CypA and CA, or mutations within the CypA-CA binding site (G89V) yields OMK cells permissive to HIV-1. Interestingly, HIV-1 infection with the V86P/H87Q/I91V/M96I capsid mutant was able to achieve similar levels of infection in OMK cells as does wild type HIV-1 with the addition of cyclosporine A, emphasizing that this motif allows infection despite TRIM-Cyp-CA interactions. Alternatively, the interaction between HIV-1 CA and CypA, is considered as a positive host factor in human cells. It has been proposed that CypA either “protects” the virus from endogenous restriction factors or allows proper CA core uncoating. Human cells lacking CypA or treated with cyclosporine A are highly resistant to infection by wild type HIV-1. Virus is blocked during the early stage of infection, at the pre-reverse transcription step. An important goal of human gene therapy is to efficiently deliver genes to non-dividing or quiescent cells such as hematopoietic stem cells and T-cells, respectively. Improvements on vector design such as self-inactivating LTRs, VSV-G envelope pseudotyping, various viral capsids, and enhancer elements have improved both the safety and efficiency of gene delivery. To identify capsid motifs that enhance transduction, we assessed whether the G89V and V86P/H87Q/I91V/M96I capsid motifs increased transduction efficacy in primary human cells as compared to vectors packaged with wild type HIV-1 gag/pol. Preliminary studies, at low levels of transduction (2000 pg p24 input ~1 MOI) in 293T cells, showed a 3-fold increase in GFP expression using the V86P/H87Q/I91V/M96I-gag/pol packaged vectors as compared to wild type or G89V-gag/pol vectors. Studies with primary PBMC and CD34+ hematopoietic stem cells are underway and will address whether the V86P/H87Q/I91V/M96I capsid motif will allow for greater transduction efficiency for non-cycling, quiescent and/or partially activated cells. Providing a means to enhance uniform vector transduction efficacy should allow for lower levels of vector input during transduction, thereby reducing the probability for insertional mutagenesis.