Academic literature on the topic 'C-trimer (CT)'

Cholecystokinin-2 receptors (CCK2R) are overexpressed in a variety of malignant diseases and therefore have gained certain attention for peptide receptor radionuclide imaging. Among extensive approaches to improve pharmacokinetics and metabolic stability of minigastrin (MG) based radioligands, the concept of multivalency for enhanced tumour targeting has not been investigated extensively. We therefore utilized fusarinine C (FSC) as chelating scaffold for novel mono-, di-, and trimeric bioconjugates for targeting CCK2R expression. FSC-based imaging probes were radiolabelled with positron emitting radionuclides (gallium-68 and zirconium-89) and characterized in vitro (log⁡D, IC50, and cell uptake) and in vivo (metabolic stability in BALB/c mice, biodistribution profile, and microPET/CT imaging in A431-CCK2R/A431-mock tumour xenografted BALB/c nude mice). Improved targeting did not fully correlate with the grade of multimerization. The divalent probe showed higher receptor affinity and increased CCK2R mediated cell uptake while the trimer remained comparable to the monomer. In vivo biodistribution studies 1 h after administration of the 68Ga-labelled radioligands confirmed this trend, but imaging at late time point (24 h) with 89Zr-labelled counterparts showed a clearly enhanced imaging contrast of the trimeric probe compared to the mono- and dimer. Furthermore, in vivo stability studies showed a higher metabolic stability for multimeric probes compared to the monomeric bioconjugate. In summary, we could show that FSC can be utilized as suitable scaffold for novel mono- and multivalent imaging probes for CCK2R-related malignancies with partly improved targeting properties for multivalent conjugates. The increased tumour accumulation of the trimer 24 h postinjection (p.i.) can be explained by slower clearance and increased metabolic stability of multimeric conjugates.

Simple sequence repeat length polymorphisms were utilized to examine genetic relatedness among accessions of watermelon (Citrullus lanatus (Thunb.) Matsum. &Nakai). A size-fractionated TaqI genomic library was screened for the occurrence of dimer and trimer simple sequence repeats (SSRs). A total of 96 (0.53%) SSR-bearing clones were identified and the inserts from 50 of these were sequenced. The dinucleotide repeats (CT)n and (GA)n accounted for 82% of the SSRs sequenced. PCR primer pairs flanking seven SSR loci were used to amplify SSRs from 32 morphologically variable watermelon genotypes from Africa, Europe, Asia, and Mexico and a single accession of Citrullus colocynthis from Chad. Cluster analysis of SSR length polymorphisms delineated 4 groups at the 25% level of genetic similarity. The largest group contained C. lanatus var. lanatus accessions. The second largest group contained only wild and cultivated "citron"-type or C. lanatus var. citroides accessions. The third group contained an accession tentatively identified as C. lanatus var. lanatus but which perhaps is a hybrid between C. lanatus var. lanatus and C. lanatus var. citroides. The fourth group consisted of a single accession identified as C. colocynthis. "Egusi"-type watermelons from Nigeria grouped with C. lanatus var. lanatus. The use of SSRs for watermelon germplasm characterization and genetic diversity studies is discussed.Key words: Citrullus, watermelon, simple sequence repeats, genetic diversity.

In eukaryotes, receptor tyrosine kinases (RTKs) and trimeric G proteins are two major signaling hubs. Signal transduction via trimeric G proteins has long been believed to be triggered exclusively by G protein-coupled receptors (GPCRs). This paradigm has recently been challenged by several studies on a multimodular signal transducer, Gα-Interacting Vesicle associated protein (GIV/Girdin). We recently demonstrated that GIV’s C terminus (CT) serves as a platform for dynamic association of ligand-activated RTKs with Gαi, and for noncanonical transactivation of G proteins. However, exogenous manipulation of this platform has remained beyond reach. Here we developed cell-permeable GIV-CT peptides by fusing a TAT-peptide transduction domain (TAT-PTD) to the minimal modular elements of GIV that are necessary and sufficient for activation of Gi downstream of RTKs, and used them to engineer signaling networks and alter cell behavior. In the presence of an intact GEF motif, TAT-GIV-CT peptides enhanced diverse processes in which GIV’s GEF function has previously been implicated, e.g., 2D cell migration after scratch-wounding, invasion of cancer cells, and finally, myofibroblast activation and collagen production. Furthermore, topical application of TAT-GIV-CT peptides enhanced the complex, multireceptor-driven process of wound repair in mice in a GEF-dependent manner. Thus, TAT-GIV peptides provide a novel and versatile tool to manipulate Gαi activation downstream of growth factors in a diverse array of pathophysiologic conditions.

TPS2671 Background: AU-007 is a computationally designed, monoclonal antibody that binds to IL-2 on its CD25 binding epitope. AU-007 bound IL-2 (A/IL-2) cannot bind to high affinity trimeric IL-2 receptors (IL-2R) consisting of CD25, CD122, and CD132 expressed on Tregs and vascular endothelium, but its binding to low affinity dimeric IL-2Rs (CD122 and CD132) expressed on T effector and NK cells is unhindered. Thus, AU-007 redirects endogenously produced or exogenous IL-2 (aldesleukin) towards activation of immune stimulating T effector and NK cells, while diminishing Treg activation and expansion. AU-007 will also bind and redirect newly secreted endogenous IL-2 resulting from A/IL-2 driven T cell expansion in the tumor, converting a Treg mediated autoinhibitory loop into an immune stimulating loop. AU-007 is unique in the IL-2 therapeutic field as engineered exogenous, recombinant “non-CD25” IL-2s in development cannot address the autoinhibitory effect of endogenous IL-2. Preclinically, AU-007 has been demonstrated to capture endogenous human IL-2 in vivo. AU-007 with a single low dose of IL-2 has demonstrated efficacy in multiple cancer models and has an excellent safety profile in non-human primates. Methods: This first-in-human, multicenter, open label Phase 1- 2 study evaluates the safety, tolerability, and initial efficacy of AU-007 +/- aldesleukin in patients with advanced solid tumors (CT-2021-CTN-03938-1). Phase 1 consists of 3 escalation arms each starting with a single 1+2 escalation cohort followed by 3+3 escalation cohorts to define the recommended Phase 2 dose (RP2D) or maximum tolerated dose (MTD). Patients with melanoma, renal cell carcinoma (RCC) and 17 selected solid tumors are eligible. Prior treatment with check point inhibitors is allowed. In Arm A, escalating doses of Q2w AU-007 are evaluated in sequential escalation cohorts. In Arm B, a single dose of aldesleukin is given with the initial AU-007 dose. AU-007 is given at a fixed dose Q2w with an escalating single aldesleukin dose in sequential escalation cohorts. In Arm C, AU-007 is evaluated in combination with aldesleukin, both given Q2w. AU-007 is administered at a fixed dose with an escalating dose of aldesleukin in sequential cohorts. The Phase 2 cohort expansion portion of the study evaluates the initial efficacy at the RP2D defined in escalation cohorts A, B, and C in 3 matching expansion cohorts of up to 20 patients each. Patients with advanced melanoma, RCC and other tumors including, but not limited to, Merkel Cell Carcinoma, NSCLC, and urothelial cancer are eligible. Enrolment to the study commences in Australia, with US sites planned to open later in 2022. Clinical trial information: CT-2021-CTN-03938-1.

ABSTRACT The matrix (MA) domains of HIV-1 precursor Gag (PrGag) proteins direct PrGag proteins to plasma membrane (PM) assembly sites where envelope (Env) protein trimers are incorporated into virus particles. MA targeting to PM sites is facilitated by its binding to phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2], and MA binding to cellular RNAs appears to serve a chaperone function that prevents MA from associating with intracellular membranes prior to arrival at the PI(4,5)P2-rich PM. Investigations have shown genetic evidence of an interaction between MA and the cytoplasmic tails (CTs) of Env trimers that contributes to Env incorporation into virions, but demonstrations of direct MA-CT interactions have proven more difficult. In direct binding assays, we show here that MA binds to Env CTs. Using MA mutants, matrix-capsid (MACA) proteins, and MA proteins incubated in the presence of inositol polyphosphate, we show a correlation between MA trimerization and CT binding. RNA ligands with high affinities for MA reduced MA-CT binding levels, suggesting that MA-RNA binding interferes with trimerization and/or directly or indirectly blocks MA-CT binding. Rough-mapping studies indicate that C-terminal CT helices are involved in MA binding and are in agreement with cell culture studies with replication-competent viruses. Our results support a model in which full-length HIV-1 Env trimers are captured in assembling PrGag lattices by virtue of their binding to MA trimers. IMPORTANCE The mechanism by which HIV-1 envelope (Env) protein trimers assemble into virus particles is poorly understood but involves an interaction between Env cytoplasmic tails (CTs) and the matrix (MA) domain of the structural precursor Gag (PrGag) proteins. We show here that direct binding of MA to Env CTs correlates with MA trimerization, suggesting models where MA lattices regulate CT interactions and/or MA-CT trimer-trimer associations increase the avidity of MA-CT binding. We also show that MA binding to RNA ligands impairs MA-CT binding, potentially by interfering with MA trimerization and/or directly or allosterically blocking MA-CT binding sites. Rough mapping implicated CT C-terminal helices in MA binding, in agreement with cell culture studies on MA-CT interactions. Our results indicate that targeting HIV-1 MA-CT interactions may be a promising avenue for antiviral therapy.

ABSTRACT Retroviral envelope glycoprotein (Env) is essential for the specific recognition of the host cell and the initial phase of infection. As reported for human immunodeficiency virus (HIV), the recruitment of Env into a retroviral membrane envelope is mediated through its interaction with a Gag polyprotein precursor of structural proteins. This interaction, occurring between the matrix domain (MA) of Gag and the cytoplasmic tail (CT) of the transmembrane domain of Env, takes place at the host cell plasma membrane. To determine whether the MA of Mason-Pfizer monkey virus (M-PMV) also interacts directly with the CT of Env, we mimicked the in vivo conditions in an in vitro experiment by using a CT in its physiological trimeric conformation mediated by the trimerization motif of the GCN4 yeast transcription factor. The MA protein was used at the concentration shifting the equilibrium to its trimeric form. The direct interaction between MA and CT was confirmed by a pulldown assay. Through the combination of nuclear magnetic resonance (NMR) spectroscopy and protein cross-linking followed by mass spectrometry analysis, the residues involved in mutual interactions were determined. NMR has shown that the C terminus of the CT is bound to the C-terminal part of MA. In addition, protein cross-linking confirmed the close proximity of the N-terminal part of CT and the N terminus of MA, which is enabled in vivo by their location at the membrane. These results are in agreement with the previously determined orientation of MA on the membrane and support the already observed mechanisms of M-PMV virus-like particle transport and budding. IMPORTANCE By a combination of nuclear magnetic resonance (NMR) and mass spectroscopy of cross-linked peptides, we show that in contrast to human immunodeficiency virus type 1 (HIV-1), the C-terminal residues of the unstructured cytoplasmic tail of Mason-Pfizer monkey virus (M-PMV) Env interact with the matrix domain (MA). Based on biochemical data and molecular modeling, we propose that individual cytoplasmic tail (CT) monomers of a trimeric complex bind MA molecules belonging to different neighboring trimers, which may stabilize the MA orientation at the membrane by the formation of a membrane-bound net of interlinked Gag and CT trimers. This also corresponds with the concept that the membrane-bound MA of Gag recruits Env through interaction with the full-length CT, while CT truncation during maturation attenuates the interaction to facilitate uncoating. We propose a model suggesting different arrangements of MA-CT complexes between a D-type and C-type retroviruses with short and long CTs, respectively.

ABSTRACTAn incomplete understanding of native human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) envelope glycoproteins (Envs) impedes the development of structural models of Env and vaccine design. This shortcoming is due in part to the low number of Env trimers on virus particles. For SIV, this low expression level can be counteracted by truncating the cytoplasmic tail (CT) of Env. CT truncation has been shown to increase Env incorporation into the virion and is commonly used in vaccine and imaging studies, but its effects on viral antigenicity have not been fully elucidated. To study the effects of a CT truncation of Env in viruses in similar genetic contexts, we introduced stop codons into the CT of a SIVsmE660 molecular clone and two neutralizing antibody (NAb) escape variants. These viruses shared 98% sequence identity in Env but were characterized as either tier 1 (sensitive to neutralization), tier 2 (moderately resistant to neutralization), or tier 3 (resistant to neutralization). However, the introduction of premature stop codons in Env at position Q741/Q742 converted all three transfection-derived viruses to a tier 3-like phenotype, and these viruses were uniformly resistant to neutralization by sera from infected macaques and monoclonal antibodies (MAbs). These changes in neutralization sensitivity were not accompanied by an increase in either the virion Env content of infection-derived viruses or the infectivity of transfection-derived viruses in human cells, suggesting that CT mutations may result in global changes to the Env conformation. Our results demonstrate that some CT truncations can affect viral antigenicity and, as such, may not be suitable surrogate models of native HIV/SIV Env.IMPORTANCEModifications to the SIV envelope protein (Env) are commonly used in structural and vaccine studies to stabilize and increase the expression of Env, often without consideration of effects on antigenicity. One such widespread modification is the truncation of the Env C-terminal tail. Here, we studied the effects of a particular cytoplasmic tail truncation in three SIVsm strains that have highly similar Env sequences but exhibit different sensitivities to neutralizing antibodies. After truncation of the Env CT, these viruses were all very resistant to neutralization by sera from infected macaques and monoclonal antibodies. The viruses with a truncated Env CT also did not exhibit the desired and typical increase in Env expression. These results underscore the importance of carefully evaluating the use of truncated Env as a model in HIV/SIV vaccine and imaging studies and of the continued need to find better models of native Env that contain fewer modifications.

"Zero-length" dimers of ribonuclease A, a novel type of dimers formed by two RNase A molecules bound to each other through a zero-length amide bond [Simons, B.L. et al. (2007) Proteins 66, 183-195], were analyzed, and tested for their possible in vitro cytotoxic activity. Results: (i) Besides dimers, also trimers and higher oligomers can be identified among the products of the covalently linking reaction. (ii) The "zero-length" dimers prepared by us appear not to be a unique species, as was instead reported by Simons et al. The product is heterogeneous, as shown by the involvement in the amide bond of amino and carboxyl groups others than only those belonging to Lys66 and Glu9. This is demonstrated by results obtained with two RNase A mutants, E9A and K66A. (iii) The "zero-length" dimers degrade poly(A).poly(U) (dsRNA) and yeast RNA (ssRNA): while the activity against poly(A).poly(U) increases with the increase of the oligomer's basicity, the activity towards yeast RNA decreases with the increase of oligomers' basicity, in agreement with many previous data, but in contrast with the results reported by Simons et al. (iv) No cytotoxicity against various tumor cells lines could be evidenced in RNase A "zero-length" dimers. (v) They instead become cytotoxic if cationized by conjugation with polyethylenimine [Futami, J. et al. (2005) J. Biosci. Bioengin. 99, 95-103]. However, polyethylenimine derivatives of RNase A "zero-length" dimers and native, monomeric RNase A are equally cytotoxic. In other words, protein "dimericity" does not play any role in this case. Moreover, (vi) cytotoxicity seems not to be specific for tumor cells: polyethylenimine-cationized native RNase A is also cytotoxic towards human monocytes.
"Zero-length" dimers of ribonuclease A, a novel type of dimers formed by two RNase A molecules bound to each other through a zero-length amide bond [Simons, B.L. et al. (2007) Proteins 66, 183-195], were analyzed, and tested for their possible in vitro cytotoxic activity. Results: (i) Besides dimers, also trimers and higher oligomers can be identified among the products of the covalently linking reaction. (ii) The "zero-length" dimers prepared by us appear not to be a unique species, as was instead reported by Simons et al. The product is heterogeneous, as shown by the involvement in the amide bond of amino and carboxyl groups others than only those belonging to Lys66 and Glu9. This is demonstrated by results obtained with two RNase A mutants, E9A and K66A. (iii) The "zero-length" dimers degrade poly(A).poly(U) (dsRNA) and yeast RNA (ssRNA): while the activity against poly(A).poly(U) increases with the increase of the oligomer's basicity, the activity towards yeast RNA decreases with the increase of oligomers' basicity, in agreement with many previous data, but in contrast with the results reported by Simons et al. (iv) No cytotoxicity against various tumor cells lines could be evidenced in RNase A "zero-length" dimers. (v) They instead become cytotoxic if cationized by conjugation with polyethylenimine [Futami, J. et al. (2005) J. Biosci. Bioengin. 99, 95-103]. However, polyethylenimine derivatives of RNase A "zero-length" dimers and native, monomeric RNase A are equally cytotoxic. In other words, protein "dimericity" does not play any role in this case. Moreover, (vi) cytotoxicity seems not to be specific for tumor cells: polyethylenimine-cationized native RNase A is also cytotoxic towards human monocytes.