Journal articles: 'Protein loop modelling'

1

Michalsky, E., A. Goede, and R. Preissner. "Loops In Proteins (LIP)--a comprehensive loop database for homology modelling." Protein Engineering Design and Selection 16, no. 12 (December 1, 2003): 979–85. http://dx.doi.org/10.1093/protein/gzg119.

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Thanki, N., J. P. Zeelen, M. Mathieu, R. Jaenicke, R. A. Abagyan, R. K. Wierenga, and W. Schliebs. "Protein engineering with monomeric triosephosphate isomerase (monoTIM): the modelling and structure verification of a seven-residue loop." Protein Engineering Design and Selection 10, no. 2 (February 1, 1997): 159–67. http://dx.doi.org/10.1093/protein/10.2.159.

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MacDonald, James T., Lawrence A. Kelley, and Paul S. Freemont. "Validating a Coarse-Grained Potential Energy Function through Protein Loop Modelling." PLoS ONE 8, no. 6 (June 18, 2013): e65770. http://dx.doi.org/10.1371/journal.pone.0065770.

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Sowdhamini, R., C. Ramakrishnan, and P. Balaram. "Modelling multiple disulphide loop containing polypeptides by random conformation generation. The test cases of α-conotoxin GI and edothelin I." "Protein Engineering, Design and Selection" 6, no. 8 (1993): 873–82. http://dx.doi.org/10.1093/protein/6.8.873.

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Tata, Rolland B., Ali F. Alsulami, Olivier Sheik Amamuddy, Tom L. Blundell, and Özlem Tastan Bishop. "Slipknot or Crystallographic Error: A Computational Analysis of the Plasmodium falciparum DHFR Structural Folds." International Journal of Molecular Sciences 23, no. 3 (January 28, 2022): 1514. http://dx.doi.org/10.3390/ijms23031514.

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The presence of protein structures with atypical folds in the Protein Data Bank (PDB) is rare and may result from naturally occurring knots or crystallographic errors. Proper characterisation of such folds is imperative to understanding the basis of naturally existing knots and correcting crystallographic errors. If left uncorrected, such errors can frustrate downstream experiments that depend on the structures containing them. An atypical fold has been identified in P. falciparum dihydrofolate reductase (PfDHFR) between residues 20–51 (loop 1) and residues 191–205 (loop 2). This enzyme is key to drug discovery efforts in the parasite, necessitating a thorough characterisation of these folds. Using multiple sequence alignments (MSA), a unique insert was identified in loop 1 that exacerbates the appearance of the atypical fold-giving it a slipknot-like topology. However, PfDHFR has not been deposited in the knotted proteins database, and processing its structure failed to identify any knots within its folds. The application of protein homology modelling and molecular dynamics simulations on the DHFR domain of P. falciparum and those of two other organisms (E. coli and M. tuberculosis) that were used as molecular replacement templates in solving the PfDHFR structure revealed plausible unentangled or open conformations of these loops. These results will serve as guides for crystallographic experiments to provide further insights into the atypical folds identified.

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Studer, Gabriel, Gerardo Tauriello, Stefan Bienert, Marco Biasini, Niklaus Johner, and Torsten Schwede. "ProMod3—A versatile homology modelling toolbox." PLOS Computational Biology 17, no. 1 (January 28, 2021): e1008667. http://dx.doi.org/10.1371/journal.pcbi.1008667.

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Computational methods for protein structure modelling are routinely used to complement experimental structure determination, thus they help to address a broad spectrum of scientific questions in biomedical research. The most accurate methods today are based on homology modelling, i.e. detecting a homologue to the desired target sequence that can be used as a template for modelling. Here we present a versatile open source homology modelling toolbox as foundation for flexible and computationally efficient modelling workflows. ProMod3 is a fully scriptable software platform that can perform all steps required to generate a protein model by homology. Its modular design aims at fast prototyping of novel algorithms and implementing flexible modelling pipelines. Common modelling tasks, such as loop modelling, sidechain modelling or generating a full protein model by homology, are provided as production ready pipelines, forming the starting point for own developments and enhancements. ProMod3 is the central software component of the widely used SWISS-MODEL web-server.

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Jezierski, G., and M. Pasenkiewicz-Gierula. "The effect of the Glu342Lys mutation in alpha1-antitrypsin on its structure, studied by molecular modelling methods." Acta Biochimica Polonica 48, no. 1 (March 31, 2001): 65–75. http://dx.doi.org/10.18388/abp.2001_5112.

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The structure of native alpha1-antitrypsin, the most abundant protease inhibitor in human plasma, is characterised primarily by a reactive loop containing the centre of proteinase inhibition, and a beta-sheet composed of five strands. Mobility of the reactive loop is confined as a result of electrostatic interactions between side chains of Glu342 and Lys290, both located at the junction of the reactive loop and the beta structure. The most common mutation in the protein, resulting in its inactivation, is Glu342-->Lys, named the Z mutation. The main goal of this work was to investigate the influence of the Z mutation on the structure of alpha1-antitrypsin. Commonly used molecular modelling methods have been applied in a comparative study of two protein models: the wild type and the Z mutant. The results indicate that the Z mutation introduces local instabilities in the region of the reactive loop. Moreover, even parts of the protein located far apart from the mutation region are affected. The Z mutation causes a relative change in the total energy of about 3%. Relatively small root mean square differences between the optimised structures of the wild type and the Z mutant, together with detailed analysis of 'conformational searching' process, lead to the hypothesis that the Z mutation principally induces a change in the dynamics of alpha1-antitrypsin.

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Collura, V. P., P. J. Greaney, and B. Robson. "A method for rapidly assessing and refining simple solvent treatments in molecular modelling. Example studies on the antigen-combining loop H2 from FAB fragment McPC603." "Protein Engineering, Design and Selection" 7, no. 2 (1994): 221–33. http://dx.doi.org/10.1093/protein/7.2.221.

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Huang, Qi, Monika Tokmina-Lukaszewska, Lewis E. Johnson, Hayden Kallas, Bojana Ginovska, John W. Peters, Lance C. Seefeldt, Brian Bothner, and Simone Raugei. "Mechanical coupling in the nitrogenase complex." PLOS Computational Biology 17, no. 3 (March 4, 2021): e1008719. http://dx.doi.org/10.1371/journal.pcbi.1008719.

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The enzyme nitrogenase reduces dinitrogen to ammonia utilizing electrons, protons, and energy obtained from the hydrolysis of ATP. Mo-dependent nitrogenase is a symmetric dimer, with each half comprising an ATP-dependent reductase, termed the Fe Protein, and a catalytic protein, known as the MoFe protein, which hosts the electron transfer P-cluster and the active-site metal cofactor (FeMo-co). A series of synchronized events for the electron transfer have been characterized experimentally, in which electron delivery is coupled to nucleotide hydrolysis and regulated by an intricate allosteric network. We report a graph theory analysis of the mechanical coupling in the nitrogenase complex as a key step to understanding the dynamics of allosteric regulation of nitrogen reduction. This analysis shows that regions near the active sites undergo large-scale, large-amplitude correlated motions that enable communications within each half and between the two halves of the complex. Computational predictions of mechanically regions were validated against an analysis of the solution phase dynamics of the nitrogenase complex via hydrogen-deuterium exchange. These regions include the P-loops and the switch regions in the Fe proteins, the loop containing the residue β-188Ser adjacent to the P-cluster in the MoFe protein, and the residues near the protein-protein interface. In particular, it is found that: (i) within each Fe protein, the switch regions I and II are coupled to the [4Fe-4S] cluster; (ii) within each half of the complex, the switch regions I and II are coupled to the loop containing β-188Ser; (iii) between the two halves of the complex, the regions near the nucleotide binding pockets of the two Fe proteins (in particular the P-loops, located over 130 Å apart) are also mechanically coupled. Notably, we found that residues next to the P-cluster (in particular the loop containing β-188Ser) are important for communication between the two halves.

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Ledoux, Julie, Maxim Stolyarchuk, Enki Bachelier, Alain Trouvé, and Luba Tchertanov. "Human Vitamin K Epoxide Reductase as a Target of Its Redox Protein." International Journal of Molecular Sciences 23, no. 7 (March 31, 2022): 3899. http://dx.doi.org/10.3390/ijms23073899.

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Human vitamin K epoxide reductase (hVKORC1) enzymatic activity requires an initial activation by a specific redox protein, a less studied step in the hVKORC1 vital cycle. Significant steric conditions must be met by enzymes, being that to adapt their configurations is mandatory for hVKORC1 activation. We studied, by molecular dynamics (MD) simulations, the folding and conformational plasticity of hVKORC1 in its inactive (fully oxidised) state using available structures, crystallographic and from de novo modelling. According to the obtained results, hVKORC1 is a modular protein composed of the stable transmembrane domain (TMD) and intrinsically disordered luminal (L) loop, possessing the great plasticity/adaptability required to perform various steps of the activation process. The docking (HADDOCK) of Protein Disulfide Isomerase (PDI) onto different hVKORC1 conformations clearly indicated that the most interpretable solutions were found on the target closed L-loop form, a prevalent conformation of hVKORC1’s oxidised state. We also suggest that the cleaved L-loop is an appropriate entity to study hVKORC1 recognition/activation by its redox protein. Additionally, the application of hVKORC1 (membrane protein) in aqueous solution is likely to prove to be very useful in practice in either in silico studies or in vitro experiments.

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Rovina, Philipp, Markus Jaritz, Siegfried Höfinger, Christine Graf, Piroska Dévay, Andreas Billich, Thomas Baumruker, and Frédéric Bornancin. "A critical β6–β7 loop in the pleckstrin homology domain of ceramide kinase." Biochemical Journal 400, no. 2 (November 14, 2006): 255–65. http://dx.doi.org/10.1042/bj20060316.

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CerK (ceramide kinase) produces ceramide 1-phosphate, a sphingophospholipid with recognized signalling properties. It localizes to the Golgi complex and fractionates essentially between detergent-soluble and -insoluble fractions; however, the determinants are unknown. Here, we made a detailed mutagenesis study of the N-terminal PH domain (pleckstrin homology domain) of CerK, based on modelling, and identified key positively charged amino acid residues within an unusual motif in the loop interconnecting β-strands 6 and 7. These residues are critical for CerK membrane association and polyphosphoinositide binding and activity. Their mutagenesis results in increased thermolability, sensitivity to proteolysis, reduced apparent molecular mass as well as propensity of the recombinant mutant protein to aggregate, indicating that this loop impacts the overall conformation of the CerK protein. This is in contrast with most PH domains whose function strongly relies on charges located in the β1–β2 loop.

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Kolodny, Rachel, Leonidas Guibas, Michael Levitt, and Patrice Koehl. "Inverse Kinematics in Biology: The Protein Loop Closure Problem." International Journal of Robotics Research 24, no. 2-3 (February 2005): 151–63. http://dx.doi.org/10.1177/0278364905050352.

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13

Laurenzi, Tommaso, Luca Palazzolo, Elisa Taiana, Simona Saporiti, Omar Ben Mariem, Uliano Guerrini, Antonino Neri, and Ivano Eberini. "Molecular Modelling of NONO and SFPQ Dimerization Process and RNA Recognition Mechanism." International Journal of Molecular Sciences 23, no. 14 (July 10, 2022): 7626. http://dx.doi.org/10.3390/ijms23147626.

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NONO and SFPQ are involved in multiple nuclear processes (e.g., pre-mRNA splicing, DNA repair, and transcriptional regulation). These proteins, along with NEAT1, enable paraspeckle formation, thus promoting multiple myeloma cell survival. In this paper, we investigate NONO and SFPQ dimer stability, highlighting the hetero- and homodimer structural differences, and model their interactions with RNA, simulating their binding to a polyG probe mimicking NEAT1guanine-rich regions. We demonstrated in silico that NONO::SFPQ heterodimerization is a more favorable process than homodimer formation. We also show that NONO and SFPQ RRM2 subunits are primarily required for protein–protein interactions with the other DBHS protomer. Simulation of RNA binding to NONO and SFPQ, beside validating RRM1 RNP signature importance, highlighted the role of β2 and β4 strand residues for RNA specific recognition. Moreover, we demonstrated the role of the NOPS region and other protomer’s RRM2 β2/β3 loop in strengthening the interaction with RNA. Our results, having deepened RNA and DBHS dimer interactions, could contribute to the design of small molecules to modulate the activity of these proteins. RNA-mimetics, able to selectively bind to NONO and/or SFPQ RNA-recognition site, could impair paraspeckle formation, thus representing a first step towards the discovery of drugs for multiple myeloma treatment.

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Wang, Guiyuan, and Zhuoqin Yang. "Stability and Hopf Bifurcation Analysis in a Delayed Myc/E2F/miR-17-92 Network Involving Interlinked Positive and Negative Feedback Loops." Discrete Dynamics in Nature and Society 2018 (November 11, 2018): 1–12. http://dx.doi.org/10.1155/2018/7014789.

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MiR-17-92 plays an important role in regulating the levels of the Myc/E2F protein. In this paper, we consider a coupling network between Myc/E2F/miR-17-92 delayed negative feedback loop and Myc/E2F positive feedback loop described by a two-dimensional delay differential equation. Based on linear stability analysis and bifurcation theory, sufficient conditions for stability of equilibria and oscillatory behaviors via Hopf bifurcation are derived when choosing time delay as well as negative feedback strength associated with oscillations as bifurcation parameters, respectively. Furthermore, direction and stability of Hopf bifurcation of time delay are studied by using the normal form method and center manifold theorem. Finally, several numerical simulations are performed to verify the results we obtained.

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Abbass, Jad, and Jean-Christophe Nebel. "Rosetta and the Journey to Predict Proteins’ Structures, 20 Years on." Current Bioinformatics 15, no. 6 (November 11, 2020): 611–28. http://dx.doi.org/10.2174/1574893615999200504103643.

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For two decades, Rosetta has consistently been at the forefront of protein structure prediction. While it has become a very large package comprising programs, scripts, and tools, for different types of macromolecular modelling such as ligand docking, protein-protein docking, protein design, and loop modelling, it started as the implementation of an algorithm for ab initio protein structure prediction. The term ’Rosetta’ appeared for the first time twenty years ago in the literature to describe that algorithm and its contribution to the third edition of the community wide Critical Assessment of techniques for protein Structure Prediction (CASP3). Similar to the Rosetta stone that allowed deciphering the ancient Egyptian civilisation, David Baker and his co-workers have been contributing to deciphering ’the second half of the genetic code’. Although the focus of Baker’s team has expended to de novo protein design in the past few years, Rosetta’s ‘fame’ is associated with its fragment-assembly protein structure prediction approach. Following a presentation of the main concepts underpinning its foundation, especially sequence-structure correlation and usage of fragments, we review the main stages of its developments and highlight the milestones it has achieved in terms of protein structure prediction, particularly in CASP.

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Mellor, Greg J., Pankaj Panwar, Andrea K. Lee, Christian Steinberg, Julie A. Hathaway, Kirsten Bartels, Susan Christian, et al. "Type 8 long QT syndrome: pathogenic variants in CACNA1C-encoded Cav1.2 cluster in STAC protein binding site." EP Europace 21, no. 11 (August 13, 2019): 1725–32. http://dx.doi.org/10.1093/europace/euz215.

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Abstract Aims Pathogenic gain-of-function variants in CACAN1C cause type-8 long QT syndrome (LQT8). We sought to describe the electrocardiographic features in LQT8 and utilize molecular modelling to gain mechanistic insights into its genetic culprits. Methods and results Rare variants in CACNA1C were identified from genetic testing laboratories. Treating physicians provided clinical information. Variant pathogenicity was independently assessed according to recent guidelines. Pathogenic (P) and likely pathogenic (LP) variants were mapped onto a 3D modelled structure of the Cav1.2 protein. Nine P/LP variants, identified in 23 patients from 19 families with non-syndromic LQTS were identified. Six variants, found in 79% of families, clustered to a 4-residue section in the cytosolic II–III loop region which forms a region capable of binding STAC SH3 domains. Therefore, variants may affect binding of SH3-domain containing proteins. Arrhythmic events occurred in similar proportions of patients with II–III loop variants and with other P/LP variants (53% vs. 48%, P = 0.41) despite shorter QTc intervals (477 ± 31 ms vs. 515 ± 37 ms, P = 0.03). A history of sudden death was reported only in families with II–III loop variants (60% vs. 0%, P = 0.03). The predominant T-wave morphology was a late peaking T wave with a steep descending limb. Exercise testing demonstrated QTc prolongation on standing and at 4 min recovery after exercise. Conclusion The majority of P/LP variants in patients with CACNA1C-mediated LQT8 cluster in an SH3-binding domain of the cytosolic II–III loop. This represents a ‘mutation hotspot’ in LQT8. A late-peaking T wave with a steep descending limb and QT prolongation on exercise are commonly seen.

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Bernard, Samuel, Branka Čajavec, Laurent Pujo-Menjouet, Michael C. Mackey, and Hanspeter Herzel. "Modelling transcriptional feedback loops: the role of Gro/TLE1 in Hes1 oscillations." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 364, no. 1842 (March 21, 2006): 1155–70. http://dx.doi.org/10.1098/rsta.2006.1761.

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The transcriptional repressor Hes1, a basic helix-loop-helix family protein, periodically changes its expression in the presomitic mesoderm. Its periodic pattern of expression is retained in a number of cultured murine cell lines. In this paper, we introduce an extended mathematical model for Hes1 oscillatory expression that includes regulation of Hes1 transcription by Drosophila Groucho (Gro) or its vertebrate counterpart, the transducine-like enhancer of split/Groucho-related gene product 1 (TLE1). Gro/TLE1 is a necessary corepressor required by a number of DNA-binding transcriptional repressors, including Hes1. Models of direct repression via Hes1 typically display an expression overshoot after transcription initiation which is not seen in the experimental data. However, numerical simulation and theoretical predictions of our model show that the cofactor Gro/TLE1 reduces the overshoot and is thus necessary for a rapid and finely tuned response of Hes1 to activation signals. Further, from detailed linear stability and numerical bifurcation analysis and simulations, we conclude that the cooperativity coefficient ( h ) for Hes1 self-repression should be large (i.e. h ≥4). Finally, we introduce the characteristic turnaround duration, and show that for our model the duration of the repression loop is between 40 and 60 min.

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Woolley, Michael J., Harriet A. Watkins, Bruck Taddese, Z. Gamze Karakullukcu, James Barwell, Kevin J. Smith, Debbie L. Hay, David R. Poyner, Christopher A. Reynolds, and Alex C. Conner. "The role of ECL2 in CGRP receptor activation: a combined modelling and experimental approach." Journal of The Royal Society Interface 10, no. 88 (November 6, 2013): 20130589. http://dx.doi.org/10.1098/rsif.2013.0589.

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The calcitonin gene-related peptide (CGRP) receptor is a complex of a calcitonin receptor-like receptor (CLR), which is a family B G-protein-coupled receptor (GPCR) and receptor activity modifying protein 1. The role of the second extracellular loop (ECL2) of CLR in binding CGRP and coupling to Gs was investigated using a combination of mutagenesis and modelling. An alanine scan of residues 271–294 of CLR showed that the ability of CGRP to produce cAMP was impaired by point mutations at 13 residues; most of these also impaired the response to adrenomedullin (AM). These data were used to select probable ECL2-modelled conformations that are involved in agonist binding, allowing the identification of the likely contacts between the peptide and receptor. The implications of the most likely structures for receptor activation are discussed.

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Macdonald, Andrew, Sabine Mazaleyrat, Christopher McCormick, Andrew Street, Nicholas J. Burgoyne, Richard M. Jackson, Virginie Cazeaux, Holly Shelton, Kalle Saksela, and Mark Harris. "Further studies on hepatitis C virus NS5A–SH3 domain interactions: identification of residues critical for binding and implications for viral RNA replication and modulation of cell signalling." Journal of General Virology 86, no. 4 (April 1, 2005): 1035–44. http://dx.doi.org/10.1099/vir.0.80734-0.

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The NS5A protein of hepatitis C virus has been shown to interact with a subset of Src homology 3 (SH3) domain-containing proteins. The molecular mechanisms underlying these observations have not been fully characterized, therefore a previous analysis of NS5A–SH3 domain interactions was extended. By using a semi-quantitative ELISA assay, a hierarchy of binding between various SH3 domains for NS5A was demonstrated. Molecular modelling of a polyproline motif within NS5A (termed PP2.2) bound to the FynSH3 domain predicted that the specificity-determining RT-loop region within the SH3 domain did not interact directly with the PP2.2 motif. However, it was demonstrated that the RT loop did contribute to the specificity of binding, implicating the involvement of other intermolecular contacts between NS5A and SH3 domains. The modelling analysis also predicted a critical role for a conserved arginine located at the C terminus of the PP2.2 motif; this was confirmed experimentally. Finally, it was demonstrated that, in comparison with wild-type replicon cells, inhibition of the transcription factor AP-1, a function previously assigned to NS5A, was not observed in cells harbouring a subgenomic replicon containing a mutation within the PP2.2 motif. However, the ability of the mutated replicon to establish itself within Huh-7 cells was unaffected. The highly conserved nature of the PP2.2 motif within NS5A suggests that functions involving this motif are of importance, but are unlikely to play a role in replication of the viral RNA genome. It is more likely that they play a role in altering the cellular environment to favour viral persistence.

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Sardiñas, Gretel, Daniel Yero, Yanet Climent, Evelin Caballero, Karem Cobas, and Olivia Niebla. "Neisseria meningitidis antigen NMB0088: sequence variability, protein topology and vaccine potential." Journal of Medical Microbiology 58, no. 2 (February 1, 2009): 196–208. http://dx.doi.org/10.1099/jmm.0.004820-0.

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The significance of Neisseria meningitidis serogroup B membrane proteins as vaccine candidates is continually growing. Here, we studied different aspects of antigen NMB0088, a protein that is abundant in outer-membrane vesicle preparations and is thought to be a surface protein. The gene encoding protein NMB0088 was sequenced in a panel of 34 different meningococcal strains with clinical and epidemiological relevance. After this analysis, four variants of NMB0088 were identified; the variability was confined to three specific segments, designated VR1, VR2 and VR3. Secondary structure predictions, refined with alignment analysis and homology modelling using FadL of Escherichia coli, revealed that almost all the variable regions were located in extracellular loop domains. In addition, the NMB0088 antigen was expressed in E. coli and a procedure for obtaining purified recombinant NMB0088 is described. The humoral immune response elicited in BALB/c mice was measured by ELISA and Western blotting, while the functional activity of these antibodies was determined in a serum bactericidal assay and an animal protection model. After immunization in mice, the recombinant protein was capable of inducing a protective response when it was administered inserted into liposomes. According to our results, the recombinant NMB0088 protein may represent a novel antigen for a vaccine against meningococcal disease. However, results from the variability study should be considered for designing a cross-protective formulation in future studies.

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SOH, Yunjo, Byoung J. SONG, Jiingjau JENG, and Abraham T. KALLARAKAL. "Critical role of Arg433 in rat transketolase activity as probed by site-directed mutagenesis." Biochemical Journal 333, no. 2 (July 15, 1998): 367–72. http://dx.doi.org/10.1042/bj3330367.

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It has been shown that one arginine per monomer at an unknown position is essential for enzyme activity of the homodimeric transketolase (TK) [Kremer, Egan and Sable (1980) J. Biol. Chem. 255, 2405–2410]. To identify the critical arginine, four highly conserved arginine residues of rat TK (Arg102, Arg350, Arg433 and Arg506) were replaced with alanine by site-directed mutagenesis. Wild-type and mutant TK proteins were produced in Escherichia coli and characterized. The Arg102 → Ala mutant exhibited similar catalytic activity to the wild-type enzyme, whereas Arg350 → Ala, Arg506 → Ala and Arg433 → Ala mutants exhibited 36.7, 37.0 and 6.1% of the wild-type activity respectively. Three recombinant proteins (wild-type, Arg350 → Ala and Arg433 → Ala) were purified to apparent homogeneity using Ni2+-affinity chromatography and further characterized. All these proteins were able to form homodimers (148 kDa), as shown by immunoblot analysis subsequent to non-denaturing gel electrophoresis. The Arg433 → Ala mutant protein was less stable than the wild-type and Arg350 → Ala proteins at 55 °C. Kinetic analyses revealed that both Vmax and Km values were markedly affected in the Arg433 → Ala mutant. The Km values for two substrates xylulose 5-phosphate and ribose 5-phosphate were 11.5- and 24.3-fold higher respectively. The kcat/Km values of the Arg433 → Ala mutant for the two substrates were less than 1% of those of the wild-type protein. Molecular modelling of the rat TK revealed that Arg433 of one monomer has three potential hydrogen-bond interactions with the catalytically important highly conserved loop of the other monomer. Thus, our biochemical analyses and modelling data suggest the critical role of the previously uncharacterized Arg433 in TK activity.

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Jeong, Dae Gwin, Chun Hua Wei, Bonsu Ku, Tae Jin Jeon, Pham Ngoc Chien, Jae Kwan Kim, So Ya Park, et al. "The family-wide structure and function of human dual-specificity protein phosphatases." Acta Crystallographica Section D Biological Crystallography 70, no. 2 (January 29, 2014): 421–35. http://dx.doi.org/10.1107/s1399004713029866.

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Dual-specificity protein phosphatases (DUSPs), which dephosphorylate both phosphoserine/threonine and phosphotyrosine, play vital roles in immune activation, brain function and cell-growth signalling. A family-wide structural library of human DUSPs was constructed based on experimental structure determination supplemented with homology modelling. The catalytic domain of each individual DUSP has characteristic features in the active site and in surface-charge distribution, indicating substrate-interaction specificity. The active-site loop-to-strand switch occurs in a subtype-specific manner, indicating that the switch process is necessary for characteristic substrate interactions in the corresponding DUSPs. A comprehensive analysis of the activity–inhibition profile and active-site geometry of DUSPs revealed a novel role of the active-pocket structure in the substrate specificity of DUSPs. A structure-based analysis of redox responses indicated that the additional cysteine residues are important for the protection of enzyme activity. The family-wide structures of DUSPs form a basis for the understanding of phosphorylation-mediated signal transduction and the development of therapeutics.

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Jiang, Leanne, and Shyuan T. Ngo. "Altered TDP-43 Structure and Function: Key Insights into Aberrant RNA, Mitochondrial, and Cellular and Systemic Metabolism in Amyotrophic Lateral Sclerosis." Metabolites 12, no. 8 (July 29, 2022): 709. http://dx.doi.org/10.3390/metabo12080709.

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Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neuromuscular disorder with no cure available and limited treatment options. ALS is a highly heterogeneous disease, whereby patients present with vastly different phenotypes. Despite this heterogeneity, over 97% of patients will exhibit pathological TAR-DNA binding protein-43 (TDP-43) cytoplasmic inclusions. TDP-43 is a ubiquitously expressed RNA binding protein with the capacity to bind over 6000 RNA and DNA targets—particularly those involved in RNA, mitochondrial, and lipid metabolism. Here, we review the unique structure and function of TDP-43 and its role in affecting the aforementioned metabolic processes in ALS. Considering evidence published specifically in TDP-43-relevant in vitro, in vivo, and ex vivo models we posit that TDP-43 acts in a positive feedback loop with mRNA transcription/translation, stress granules, cytoplasmic aggregates, and mitochondrial proteins causing a relentless cycle of disease-like pathology eventuating in neuronal toxicity. Given its undeniable presence in ALS pathology, TDP-43 presents as a promising target for mechanistic disease modelling and future therapeutic investigations.

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Sajid, Moon, Shane R. Stone, and Parwinder Kaur. "Phylogenetic Analysis and Protein Modelling of Isoflavonoid Synthase Highlights Key Catalytic Sites towards Realising New Bioengineering Endeavours." Bioengineering 9, no. 11 (October 24, 2022): 609. http://dx.doi.org/10.3390/bioengineering9110609.

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Isoflavonoid synthase (IFS) is a critical enzyme for the biosynthesis of over 2400 isoflavonoids. Isoflavonoids are an important class of plant secondary metabolites that have a range of pharmaceutical and nutraceutical properties. With growing interest in isoflavonoids from both research and industrial perspectives, efforts are being forwarded to enhance isoflavonoid production in-planta and ex-planta; therefore, in-silico analysis and characterisation of available IFS protein sequences are needed. The present study is the first-ever attempt toward phylogenetic analysis and protein modelling of available IFS protein sequences. Phylogenetic analysis has shown that IFS amino acid sequences have 86.4% pairwise identity and 26.5% identical sites, and the sequences were grouped into six different clades. The presence of a β-hairpin and extra loop at catalytic sites of Trifolium pratense, Beta vulgaris and Medicago truncatula, respectively, compared with Glycyrrhiza echinata are critical structural differences that may affect catalytic function. Protein docking highlighted the preference of selected IFS for liquiritigenin compared with naringenin and has listed T. pratense as the most efficient candidate for heterologous biosynthesis of isoflavonoids. The in-silico characterisation of IFS represented in this study is vital in realising the new bioengineering endeavours and will help in the characterisation and selection of IFS candidate enzymes for heterologous biosynthesis of isoflavonoids.

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Mishra, Manasi, Vigyasa Singh, Meenakshi B. Tellis, Rakesh S. Joshi, and Shailja Singh. "Repurposing the McoTI-II Rigid Molecular Scaffold in to Inhibitor of ‘Papain Superfamily’ Cysteine Proteases." Pharmaceuticals 14, no. 1 (December 23, 2020): 7. http://dx.doi.org/10.3390/ph14010007.

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Clan C1A or ‘papain superfamily’ cysteine proteases are key players in many important physiological processes and diseases in most living systems. Novel approaches towards the development of their inhibitors can open new avenues in translational medicine. Here, we report a novel design of a re-engineered chimera inhibitor Mco-cysteine protease inhibitor (CPI) to inhibit the activity of C1A cysteine proteases. This was accomplished by grafting the cystatin first hairpin loop conserved motif (QVVAG) onto loop 1 of the ultrastable cyclic peptide scaffold McoTI-II. The recombinantly expressed Mco-CPI protein was able to bind with micromolar affinity to papain and showed remarkable thermostability owing to the formation of multi-disulphide bonds. Using an in silico approach based on homology modelling, protein–protein docking, the calculation of the free-energy of binding, the mechanism of inhibition of Mco-CPI against representative C1A cysteine proteases (papain and cathepsin L) was validated. Furthermore, molecular dynamics simulation of the Mco-CPI–papain complex validated the interaction as stable. To conclude, in this McoTI-II analogue, the specificity had been successfully redirected towards C1A cysteine proteases while retaining the moderate affinity. The outcomes of this study pave the way for further modifications of the Mco-CPI design for realizing its full potential in therapeutics. This study also demonstrates the relevance of ultrastable peptide-based scaffolds for the development of novel inhibitors via grafting.

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Sajnaga, Ewa, Konrad Kubiński, and Ryszard Szyszka. "Catalytic activity of mutants of yeast protein kinase CK2alpha." Acta Biochimica Polonica 55, no. 4 (November 17, 2008): 767–76. http://dx.doi.org/10.18388/abp.2008_3039.

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Yeast CK2 is a highly conserved member of the protein kinase CGMC subfamily composed of two catalytic (alpha and alpha') and two regulatory (beta and beta') subunits. The amino-acid sequences of both catalytic subunits are only 60% homologous. Modelling of the tertiary structure of the CK2alpha displays additional alpha-helical structures not present in the CK2alpha' subunit, connecting the ATP-binding loop with the catalytic and activation loops. Deletion of this part causes drastic structural and enzymatic changes of the protein (CK2alpha(Delta91-128)) with characteristics similar to yeast CK2alpha' (low sensitivity to salt, heparin and spermine). Additionally, the deletion causes an over 5-fold decrease of the binding affinity for ATP and ATP-competitive inhibitors (TBBt and TBBz). The structural basis for TBBt and TBBz selectivity is provided by the hydrophobic pocket adjacent to the ATP/GTP binding site, which is smaller in CK2 than in the majority of other protein kinases. The importance of hydrophobic interactions in the binding of specific inhibitors was investigated here by mutational analysis of CK2alpha residues whose side chains contribute to reducing the size of the hydrophobic pocket. Site-directed mutagenesis was used to replace Val67 and Ile213 by Ala. The kinetic properties of the single mutants CK2alpha(Val67Ala) and CK2alpha(Ile213Ala), and the double mutant CK2(Val67Ala Ile213Ala) were studied with respect to ATP, and both inhibitors TBBt and TBBz. The K(m) values for ATP did not change or were very close to those of the parental kinase. In contrast, all CK2alpha mutants analysed displayed higher K(i) values towards the inhibitors (10 to 12-fold higher with TBBt and 3 to 6-fold with TBBt) comparing to recombinant wild-type CK2alpha.

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RAJAMOHAN, Govindan, Monika DAHIYA, Shekhar C. MANDE, and Kanak L. DIKSHIT. "Function of the 90-loop (Thr90–Glu100) region of staphylokinase in plasminogen activation probed through site-directed mutagenesis and loop deletion." Biochemical Journal 365, no. 2 (July 15, 2002): 379–89. http://dx.doi.org/10.1042/bj20011647.

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Staphylokinsae (SAK) forms a bimolecular complex with human plasmin(ogen) and changes its substrate specificity by exposing new exosites that enhances accession of substrate plasminogen (PG) to the plasmin (Pm) active site. Protein modelling studies indicated the crucial role of a loop in SAK (SAK 90-loop; Thr90—Glu100) for the docking of the substrate PG to the SAK—Pm complex. Function of SAK 90-loop was studied by site-directed mutagenesis and loop deletion. Deletion of nine amino acid residues (Tyr92—Glu100) from the SAK 90-loop, resulted in ≈60% reduction in the PG activation, but it retained the ability to generate an active site within the complex of loop mutant of SAK (SAKΔ90) and Pm. The preformed activator complex of SAKΔ90 with Pm, however, displayed a 50–60% reduction in substrate PG activation that remained unaffected in the presence of kringle domains (K1+K2+K3+K4) of PG, whereas PG activation by SAK—Pm complex displayed ∼50% reduction in the presence of kringles, suggesting the involvement of the kringle domains in modulating the PG activation by native SAK but not by SAKΔ90. Lysine residues (Lys94, Lys96, Lys97 and Lys98) of the SAK 90-loop were individually mutated into alanine and, among these four SAK loop mutants, SAKK97A and SAKK98A exhibited specific activities about one-third and one-quarter respectively of the native SAK. The kinetic parameters of PG activation of their 1:1 complex with Pm indicated that the Km values of PG towards the activator complex of these two SAK mutants were 4–6-fold higher, suggesting the decreased accessibility of the substrate PG to the activator complex formed by these SAK mutants. These results demonstrated the involvement of the Lys97 and Lys98 residues of the SAK 90-loop in assisting the interaction with substrate PG. These interactions of SAK—Pm activator complex via the SAK 90-loop may provide additional anchorage site(s) to the substrate PG that, in turn, may promote the overall process of SAK-mediated PG activation.

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Chowdhury, Sourav, Dwipanjan Sanyal, Sagnik Sen, Vladimir N. Uversky, Ujjwal Maulik, and Krishnananda Chattopadhyay. "Evolutionary Analyses of Sequence and Structure Space Unravel the Structural Facets of SOD1." Biomolecules 9, no. 12 (December 4, 2019): 826. http://dx.doi.org/10.3390/biom9120826.

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Superoxide dismutase (SOD) is the primary enzyme of the cellular antioxidant defense cascade. Misfolding, concomitant oligomerization, and higher order aggregation of human cytosolic SOD are linked to amyotrophic lateral sclerosis (ALS). Although, with two metal ion cofactors SOD1 is extremely robust, the de-metallated apo form is intrinsically disordered. Since the rise of oxygen-based metabolism and antioxidant defense systems are evolutionary coupled, SOD is an interesting protein with a deep evolutionary history. We deployed statistical analysis of sequence space to decode evolutionarily co-varying residues in this protein. These were validated by applying graph theoretical modelling to understand the impact of the presence of metal ion co-factors in dictating the disordered (apo) to hidden disordered (wild-type SOD1) transition. Contact maps were generated for different variants, and the selected significant residues were mapped on separate structure networks. Sequence space analysis coupled with structure networks helped us to map the evolutionarily coupled co-varying patches in the SOD1 and its metal-depleted variants. In addition, using structure network analysis, the residues with a major impact on the internal dynamics of the protein structure were investigated. Our results reveal that the bulk of these evolutionarily co-varying residues are localized in the loop regions and positioned differentially depending upon the metal residence and concomitant steric restrictions of the loops.

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George, Biju, Rajrani Ruhel, Mohit Mazumder, Veerendra Kumar Sharma, Swatantra Kumar Jain, Samudrala Gourinath, and Supriya Chakraborty. "Mutational analysis of the helicase domain of a replication initiator protein reveals critical roles of Lys 272 of the B′ motif and Lys 289 of the β-hairpin loop in geminivirus replication." Journal of General Virology 95, no. 7 (July 1, 2014): 1591–602. http://dx.doi.org/10.1099/vir.0.064923-0.

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Replication initiator protein (Rep) is indispensable for rolling-circle replication of geminiviruses, a group of plant-infecting circular ssDNA viruses. However, the mechanism of DNA unwinding by circular ssDNA virus-encoded helicases is unknown. To understand geminivirus Rep function, we compared the sequence and secondary structure of Rep with those of bovine papillomavirus E1 and employed charged residue-to-alanine scanning mutagenesis to generate a set of single-substitution mutants in Walker A (K227), in Walker B (D261, 262), and within or adjacent to the B′ motif (K272, K286 and K289). All mutants were asymptomatic and viral accumulation could not be detected by Southern blotting in both tomato and N. benthamiana plants. Furthermore, the K272 and K289 mutants were deficient in DNA binding and unwinding. Biochemical studies and modelling data based on comparisons with the known structures of SF3 helicases suggest that the conserved lysine (K289) located in a predicted β-hairpin loop may interact with ssDNA, while lysine 272 in the B′ motif (K272) located on the outer surface of the protein is presumably involved in coupling ATP-induced conformational changes to DNA binding. To the best of our knowledge, this is the first time that the roles of the B′ motif and the adjacent β-hairpin loop in geminivirus replication have been elucidated.

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Yan, Fang, Li Liu, and Qingyun Wang. "Combinatorial dynamics of protein synthesis time delay and negative feedback loop in NF-κB signalling pathway." IET Systems Biology 14, no. 5 (October 1, 2020): 284–91. http://dx.doi.org/10.1049/iet-syb.2020.0034.

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Modahl, Cassandra M., Mrinalini, Seth Frietze, and Stephen P. Mackessy. "Adaptive evolution of distinct prey-specific toxin genes in rear-fanged snake venom." Proceedings of the Royal Society B: Biological Sciences 285, no. 1884 (August 2018): 20181003. http://dx.doi.org/10.1098/rspb.2018.1003.

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Venom proteins evolve rapidly, and as a trophic adaptation are excellent models for predator–prey evolutionary studies. The key to a deeper understanding of venom evolution is an integrated approach, combining prey assays with analysis of venom gene expression and venom phenotype. Here, we use such an approach to study venom evolution in the Amazon puffing snake, Spilotes sulphureus , a generalist feeder. We identify two novel three-finger toxins: sulditoxin and sulmotoxin 1. These new toxins are not only two of the most abundant venom proteins, but are also functionally intriguing, displaying distinct prey-specific toxicities. Sulditoxin is highly toxic towards lizard prey, but is non-toxic towards mammalian prey, even at greater than 22-fold higher dosage. By contrast, sulmotoxin 1 exhibits the reverse trend. Furthermore, evolutionary analysis and structural modelling show highest sequence variability in the central loop of these proteins, probably driving taxon-specific toxicity. This is, to our knowledge, the first case in which a bimodal and contrasting pattern of toxicity has been shown for proteins in the venom of a single snake in relation to diet. Our study is an example of how toxin gene neofunctionalization can result in a venom system dominated by one protein superfamily and still exhibit flexibility in prey capture efficacy.

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Chen, Ting, Haiying Wu, Chenxi Zhang, Jiarong Feng, Linqi Chen, Rongrong Xie, Fengyun Wang, et al. "Clinical, Genetics, and Bioinformatic Characterization of Mutations Affecting an Essential Region of PLS3 in Patients with BMND18." International Journal of Endocrinology 2018 (October 14, 2018): 1–9. http://dx.doi.org/10.1155/2018/8953217.

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Background. Bone mineral density quantitative trait locus 18 (BMND18, OMIM #300910) is a type of early-onset osteogenesis imperfecta (OI) caused by loss-of-function mutations in the PLS3 gene, which encodes plastin-3, a key protein in the formation of actin bundles throughout the cytoskeleton. Here, we report a patient with PLS3 mutation caused BMND18 and evaluated all the reported disease-causing mutations by bioinformatic analysis. Methods. Targeted gene sequencing was performed to find the disease-causing mutation in our patient. Bioinformatic analyses mainly including homology modelling and molecular dynamics stimulation were conducted to explore the impact of the previously reported mutations on plastin-3. Results. Gene sequencing showed a novel nonsense mutation (c.745G > T, p.E249X), which locates at a highly conserved region containing residues p.240–266 (LOOP-1) in the PLS3 gene. Further bioinformatic analyses of the previously reported mutations revealed that LOOP-1 is predicted to physically connect the calponin-homology 1 (CH1) and CH2 domains of the ABD1 fragment and spatially locates within the interface of ABD1 and ABD2. It is crucial to the conformation transition and actin-binding function of plastin-3. Conclusions. This report identified a novel mutation that truncates the PLS3 gene. Moreover, bioinformatic analyses of the previous reported mutations in PLS3 gene lead us to find a critical LOOP-1 region of plastin-3 mutations at which may be detrimental to the integral conformation of plastin-3 and thus affect its binding to actin filament.

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Koide, Hiroki, Noriyuki Kodera, Shveta Bisht, Shoji Takada, and Tsuyoshi Terakawa. "Modeling of DNA binding to the condensin hinge domain using molecular dynamics simulations guided by atomic force microscopy." PLOS Computational Biology 17, no. 7 (July 30, 2021): e1009265. http://dx.doi.org/10.1371/journal.pcbi.1009265.

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The condensin protein complex compacts chromatin during mitosis using its DNA-loop extrusion activity. Previous studies proposed scrunching and loop-capture models as molecular mechanisms for the loop extrusion process, both of which assume the binding of double-strand (ds) DNA to the hinge domain formed at the interface of the condensin subunits Smc2 and Smc4. However, how the hinge domain contacts dsDNA has remained unknown. Here, we conducted atomic force microscopy imaging of the budding yeast condensin holo-complex and used this data as basis for coarse-grained molecular dynamics simulations to model the hinge structure in a transient open conformation. We then simulated the dsDNA binding to open and closed hinge conformations, predicting that dsDNA binds to the outside surface when closed and to the outside and inside surfaces when open. Our simulations also suggested that the hinge can close around dsDNA bound to the inside surface. Based on these simulation results, we speculate that the conformational change of the hinge domain might be essential for the dsDNA binding regulation and play roles in condensin-mediated DNA-loop extrusion.

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Ehresmann, Chantal, Claude Philippe, E. Westhof, Bernard Ehresmann, Lionel Bénard, and Claude Portier. "A pseudoknot is required for efficient translational initiation and regulation of the Escherichia coli rpsO gene coding for ribosomal protein S15." Biochemistry and Cell Biology 73, no. 11-12 (December 1, 1995): 1131–40. http://dx.doi.org/10.1139/o95-122.

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Escherichia coli ribosomal protein S15 down regulates its own synthesis by binding to its mRNA in a region overlapping the ribosome binding site, called the translational operator. This binding stabilizes a pseudoknot structure that exists in equilibrium with two stem–loop structures. When synthesized in excess over 16S rRNA, S15 binds to its translational operator and traps the ribosome on its loading site in a transient state, preventing the formation of the active ternary (30S–mRNA–rRNAfMet) complex. This inhibition can be suppressed by 16S rRNA, which displaces S15 from the mRNA. An extensive mutational analysis showed that the pseudoknot is the structural element required for S15 recognition and in vivo translational control. Specific sequence determinants are located in limited regions of the structure formed by the pseudoknot. An unexpected result is that the pseudoknot can exist in a variety of topologically equivalent structures recognizable and shapable by S15. Based on footprinting experiments and computer graphic modelling, S15 shields the two stems of the pseudoknot, sitting in the major groove of the coaxial stack.Key words: ribosomes, translational control, r-protein S15, pseudoknot, RNA–protein recognition.

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35

Ghomlaghi, Milad, Guang Yang, Sungyoung Shin, David E. James, and Lan K. Nguyen. "Dynamic modelling of the PI3K/MTOR signalling network uncovers biphasic dependence of mTORC1 activity on the mTORC2 subunit SIN1." PLOS Computational Biology 17, no. 9 (September 16, 2021): e1008513. http://dx.doi.org/10.1371/journal.pcbi.1008513.

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The PI3K/MTOR signalling network regulates a broad array of critical cellular processes, including cell growth, metabolism and autophagy. The mechanistic target of rapamycin (MTOR) kinase functions as a core catalytic subunit in two physically and functionally distinct complexes mTORC1 and mTORC2, which also share other common components including MLST8 (also known as GβL) and DEPTOR. Despite intensive research, how mTORC1 and 2 assembly and activity are coordinated, and how they are functionally linked remain to be fully characterized. This is due in part to the complex network wiring, featuring multiple feedback loops and intricate post-translational modifications. Here, we integrate predictive network modelling, in vitro experiments and -omics data analysis to elucidate the emergent dynamic behaviour of the PI3K/MTOR network. We construct new mechanistic models that encapsulate critical mechanistic details, including mTORC1/2 coordination by MLST8 (de)ubiquitination and the Akt-to-mTORC2 positive feedback loop. Model simulations validated by experimental studies revealed a previously unknown biphasic, threshold-gated dependence of mTORC1 activity on the key mTORC2 subunit SIN1, which is robust against cell-to-cell variation in protein expression. In addition, our integrative analysis demonstrates that ubiquitination of MLST8, which is reversed by OTUD7B, is regulated by IRS1/2. Our results further support the essential role of MLST8 in enabling both mTORC1 and 2’s activity and suggest MLST8 as a viable therapeutic target in breast cancer. Overall, our study reports a new mechanistic model of PI3K/MTOR signalling incorporating MLST8-mediated mTORC1/2 formation and unveils a novel regulatory linkage between mTORC1 and mTORC2.

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Bell, S., J. R. Matthews, E. Jaffray, and R. T. Hay. "I(kappa)B(gamma) inhibits DNA binding of NF-kappaB p50 homodimers by interacting with residues that contact DNA." Molecular and Cellular Biology 16, no. 11 (November 1996): 6477–85. http://dx.doi.org/10.1128/mcb.16.11.6477.

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NF-(kappa)B is an inducible transcription factor that activates many cellular genes involved in stress and immune response and whose DNA binding activity and cellular distribution are regulated by I(kappa)B inhibitor proteins. The interaction between NF-(kappa)B p50 and DNA was investigated by protein footprinting using chemical modification and partial proteolysis. Both methods confirmed lysine-DNA contacts already found in the crystal structure (K-147, K-149, K-244, K-275, and K-278) but also revealed an additional contact in the lysine cluster K-77-K-78-K-80 which was made on an extended DNA. Molecular modelling of such a DNA-protein complex revealed that lysine 80 is ideally placed to make phosphate backbone contacts in the extended DNA. Thus, it seems likely that the entire AB loop, containing lysines 77, 78, and 80, forms a C-shaped clamp that closes around the DNA recognition site. The same protein footprinting approaches were used to probe the interaction of p50 with the ankyrin repeat containing proteins I(kappa)B(gamma) and I(kappa)B(alpha). Lysine residues in p50 that were protected from modification by DNA were also protected from modification by I(kappa)B(gamma) but not I(kappa)B(alpha). Similarly, proteolytic cleavage at p50 residues which contact DNA was inhibited by bound I(kappa)B(gamma) but was enhanced by the presence of I(kappa)B(alpha). Thus, I(kappa)B(gamma) inhibits the DNA binding activity of p50 by direct interactions with residues contacting DNA, whereas the same residues remain exposed in the presence of I(kappa)B(alpha), which binds to p50 but does not block DNA binding.

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Modi, Saurabh, Supravat Dey, and Abhyudai Singh. "Noise suppression in stochastic genetic circuits using PID controllers." PLOS Computational Biology 17, no. 7 (July 28, 2021): e1009249. http://dx.doi.org/10.1371/journal.pcbi.1009249.

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Inside individual cells, protein population counts are subject to molecular noise due to low copy numbers and the inherent probabilistic nature of biochemical processes. We investigate the effectiveness of proportional, integral and derivative (PID) based feedback controllers to suppress protein count fluctuations originating from two noise sources: bursty expression of the protein, and external disturbance in protein synthesis. Designs of biochemical reactions that function as PID controllers are discussed, with particular focus on individual controllers separately, and the corresponding closed-loop system is analyzed for stochastic controller realizations. Our results show that proportional controllers are effective in buffering protein copy number fluctuations from both noise sources, but this noise suppression comes at the cost of reduced static sensitivity of the output to the input signal. In contrast, integral feedback has no effect on the protein noise level from stochastic expression, but significantly minimizes the impact of external disturbances, particularly when the disturbance comes at low frequencies. Counter-intuitively, integral feedback is found to amplify external disturbances at intermediate frequencies. Next, we discuss the design of a coupled feedforward-feedback biochemical circuit that approximately functions as a derivate controller. Analysis using both analytical methods and Monte Carlo simulations reveals that this derivative controller effectively buffers output fluctuations from bursty stochastic expression, while maintaining the static input-output sensitivity of the open-loop system. In summary, this study provides a systematic stochastic analysis of biochemical controllers, and paves the way for their synthetic design and implementation to minimize deleterious fluctuations in gene product levels.

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Qaid, Talal S., Hussein Mazaar, Mohammed S. Alqahtani, Abeer A. Raweh, and Wafaa Alakwaa. "Deep sequence modelling for predicting COVID-19 mRNA vaccine degradation." PeerJ Computer Science 7 (June 22, 2021): e597. http://dx.doi.org/10.7717/peerj-cs.597.

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The worldwide coronavirus (COVID-19) pandemic made dramatic and rapid progress in the year 2020 and requires urgent global effort to accelerate the development of a vaccine to stop the daily infections and deaths. Several types of vaccine have been designed to teach the immune system how to fight off certain kinds of pathogens. mRNA vaccines are the most important candidate vaccines because of their capacity for rapid development, high potency, safe administration and potential for low-cost manufacture. mRNA vaccine acts by training the body to recognize and response to the proteins produced by disease-causing organisms such as viruses or bacteria. This type of vaccine is the fastest candidate to treat COVID-19 but it currently facing several limitations. In particular, it is a challenge to design stable mRNA molecules because of the inefficient in vivo delivery of mRNA, its tendency for spontaneous degradation and low protein expression levels. This work designed and implemented a sequence deep model based on bidirectional GRU and LSTM models applied on the Stanford COVID-19 mRNA vaccine dataset to predict the mRNA sequences responsible for degradation by predicting five reactivity values for every position in the sequence. Four of these values determine the likelihood of degradation with/without magnesium at high pH (pH 10) and high temperature (50 degrees Celsius) and the fifth reactivity value is used to determine the likely secondary structure of the RNA sample. The model relies on two types of features, namely numerical and categorical features, where the categorical features are extracted from the mRNA sequences, structure and predicted loop. These features are represented and encoded by numbers, and then, the features are extracted using embedding layer learning. There are five numerical features depending on the likelihood for each pair of nucleotides in the RNA. The model gives promising results because it predicts the five reactivity values with a validation mean columnwise root mean square error (MCRMSE) of 0.125 using LSTM model with augmentation and the codon encoding method. Codon encoding outperforms Base encoding in MCRMSE validation error using the LSTM model meanwhile Base encoding outperforms codon encoding due to less over-fitting and the difference between the training and validation loss error is 0.008.

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Abella, Jayvee, Dinler Antunes, Cecilia Clementi, and Lydia Kavraki. "APE-Gen: A Fast Method for Generating Ensembles of Bound Peptide-MHC Conformations." Molecules 24, no. 5 (March 2, 2019): 881. http://dx.doi.org/10.3390/molecules24050881.

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The Class I Major Histocompatibility Complex (MHC) is a central protein in immunology as it binds to intracellular peptides and displays them at the cell surface for recognition by T-cells. The structural analysis of bound peptide-MHC complexes (pMHCs) holds the promise of interpretable and general binding prediction (i.e., testing whether a given peptide binds to a given MHC). However, structural analysis is limited in part by the difficulty in modelling pMHCs given the size and flexibility of the peptides that can be presented by MHCs. This article describes APE-Gen (Anchored Peptide-MHC Ensemble Generator), a fast method for generating ensembles of bound pMHC conformations. APE-Gen generates an ensemble of bound conformations by iterated rounds of (i) anchoring the ends of a given peptide near known pockets in the binding site of the MHC, (ii) sampling peptide backbone conformations with loop modelling, and then (iii) performing energy minimization to fix steric clashes, accumulating conformations at each round. APE-Gen takes only minutes on a standard desktop to generate tens of bound conformations, and we show the ability of APE-Gen to sample conformations found in X-ray crystallography even when only sequence information is used as input. APE-Gen has the potential to be useful for its scalability (i.e., modelling thousands of pMHCs or even non-canonical longer peptides) and for its use as a flexible search tool. We demonstrate an example for studying cross-reactivity.

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Li, Xiao-Quan, Li-Wen Qiu, Yue Chen, Kun Wen, Jian-Piao Cai, Jing Chen, Yu-Xian Pan, et al. "Dengue virus envelope domain III immunization elicits predominantly cross-reactive, poorly neutralizing antibodies localized to the AB loop: implications for dengue vaccine design." Journal of General Virology 94, no. 10 (October 1, 2013): 2191–201. http://dx.doi.org/10.1099/vir.0.055178-0.

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Dengue virus (DENV) is a mosquito-borne virus that causes severe health problems. An effective tetravalent dengue vaccine candidate that can provide life-long protection simultaneously against all four DENV serotypes is highly anticipated. A better understanding of the antibody response to DENV envelope protein domain III (EDIII) may offer insights into vaccine development. Here, we identified 25 DENV cross-reactive mAbs from immunization with Pichia pastoris-expressed EDIII of a single or all four serotype(s) using a prime–boost protocol, and through pepscan analysis found that 60 % of them (15/25) specifically recognized the same highly conserved linear epitope aa 309–320 of EDIII. All 15 complex-reactive mAbs exhibited significant cross-reactivity with recombinant EDIII from all DENV serotypes and also with C6/36 cells infected with DENV-1, -2, -3 and -4. However, neutralization assays indicated that the majority of these 15 mAbs were either moderately or weakly neutralizing. Through further epitope mapping by yeast surface display, two residues in the AB loop, Q316 and H317, were discovered to be critical. Three-dimensional modelling analysis suggests that this epitope is surface exposed on EDIII but less accessible on the surface of the E protein dimer and trimer, especially on the surface of the mature virion. It is concluded that EDIII as an immunogen may elicit cross-reactive mAbs toward an epitope that is not exposed on the virion surface, therefore contributing inefficiently to the mAbs neutralization potency. Therefore, the prime–boost strategy of EDIII from a single serotype or four serotypes mainly elicited a poorly neutralizing, cross-reactive antibody response to the conserved AB loop of EDIII.

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Meh, Primož, Miha Pavšič, Vito Turk, Antonio Baici, and Brigita Lenarčič. "Dual concentration-dependent activity of thyroglobulin type-1 domain of testican: specific inhibitor and substrate of cathepsin L." Biological Chemistry 386, no. 1 (January 1, 2005): 75–83. http://dx.doi.org/10.1515/bc.2005.010.

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Abstract The thyroglobulin type-1 (Tg-1) domain is a protein module that occurs in a variety of secreted and membrane proteins and is recognised as a potent inhibitor of cysteine peptidases. We present here some properties of the Tg-1 domain of human testican, a modularly organised proteoglycan secreted mainly by brain cells, the exact in vivo function of which is not yet clear. The domain was prepared as a recombinant protein in a Pichia pastoris expression system and its activity was demonstrated by specific and selective inhibition of cathepsin L (K i=0.14 nM). Interaction at high enzyme and inhibitor concentrations resulted in degradation of the domain by cathepsin L, which was not observed under conditions used for the determination of kinetic parameters. No inhibitory activity could be detected for cathepsin K, but it exhibited a very similar degradation pattern. Homology modelling provided a good explanation for the different behaviour observed with the two enzymes. Firstly, the steric fit between the interfaces of testican domain and cathepsin L is stabilised by numerous favourable forces, while no such interactions are evident in the complex with cathepsin K, and repulsive interactions even prevent access of the domain to the active site of papain. Secondly, the prolonged first loop of the domain occupies a position near the catalytic cysteine residue in a more substrate-like manner, enabling cleavage of the Gly22-Ala23 bond.

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Tang, Ke, Jinfeng Zhang, and Jie Liang. "Fast Protein Loop Sampling and Structure Prediction Using Distance-Guided Sequential Chain-Growth Monte Carlo Method." PLoS Computational Biology 10, no. 4 (April 24, 2014): e1003539. http://dx.doi.org/10.1371/journal.pcbi.1003539.

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Zhan, Jingyu, Angela R. Harrison, Stephanie Portelli, Thanh Binh Nguyen, Isshu Kojima, Siqiong Zheng, Fei Yan, et al. "Definition of the immune evasion-replication interface of rabies virus P protein." PLOS Pathogens 17, no. 7 (July 8, 2021): e1009729. http://dx.doi.org/10.1371/journal.ppat.1009729.

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Rabies virus phosphoprotein (P protein) is a multifunctional protein that plays key roles in replication as the polymerase cofactor that binds to the complex of viral genomic RNA and the nucleoprotein (N protein), and in evading the innate immune response by binding to STAT transcription factors. These interactions are mediated by the C-terminal domain of P (PCTD). The colocation of these binding sites in the small globular PCTD raises the question of how these interactions underlying replication and immune evasion, central to viral infection, are coordinated and, potentially, coregulated. While direct data on the binding interface of the PCTD for STAT1 is available, the lack of direct structural data on the sites that bind N protein limits our understanding of this interaction hub. The PCTD was proposed to bind via two sites to a flexible loop of N protein (Npep) that is not visible in crystal structures, but no direct analysis of this interaction has been reported. Here we use Nuclear Magnetic Resonance, and molecular modelling to show N protein residues, Leu381, Asp383, Asp384 and phosphor-Ser389, are likely to bind to a ‘positive patch’ of the PCTD formed by Lys211, Lys214 and Arg260. Furthermore, in contrast to previous predictions we identify a single site of interaction on the PCTD by this Npep. Intriguingly, this site is proximal to the defined STAT1 binding site that includes Ile201 to Phe209. However, cell-based assays indicate that STAT1 and N protein do not compete for P protein. Thus, it appears that interactions critical to replication and immune evasion can occur simultaneously with the same molecules of P protein so that the binding of P protein to activated STAT1 can potentially occur without interrupting interactions involved in replication. These data suggest that replication complexes might be directly involved in STAT1 antagonism.

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Shelden, Megan C., Susan M. Howitt, Brent N. Kaiser, and Stephen D. Tyerman. "Identification and functional characterisation of aquaporins in the grapevine, Vitis vinifera." Functional Plant Biology 36, no. 12 (2009): 1065. http://dx.doi.org/10.1071/fp09117.

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Plant aquaporins belong to a large superfamily of conserved proteins called the major intrinsic proteins (MIPs). There is limited information about the diversity of MIPs in grapevine, and their water transport capacity. The aim of the present study was to identify MIPs from grapevine and functionally characterise water transport of a subset of MIPs. Candidate genes were identified, by screening a Vitis vinifera L. (cv. Cabernet Sauvignon) cDNA library with gene specific probes, for aquaporin cDNAs encoding members of the plasma membrane intrinsic protein (PIP) and tonoplast intrinsic protein (TIP) subfamilies. The screen resulted in the identification of 11 full-length and two partial length aquaporin cDNAs. VvTIP2;1 isoforms had different 3′ UTRs, immediately upstream of the poly(A) tail, suggesting the presence of multiple cleavage sites for polyadenylation. Using published genome sequences of grapevine, we conducted a phylogenetic analysis of the MIPs with previously characterised MIPs from Arabidopsis. We identified 23 full-length MIP genes from the V. vinifera genome sequence of a near homozygous line (PN40024) that cluster into the four main subfamilies (and subgroups within) identified in other species. However, based on the identification of PIP2 genes in Cabernet Sauvignon that were not present in the PN40024 genome, there are likely to be more than 23 MIP genes in other heterozygous grapevine cultivars. Water transport capacity was determined for several PIPs and TIPs, by expression in Xenopus oocytes. Only VvPIP2 and VvTIP proteins function as water channels with the exception of VvPIP2;5. VvPIP2;5 differs from the water conducting VvPIP2;1 by the substitution of two highly conserved amino acids in Loop B (G97S, G100W), which was shown by homology modelling to likely form a hydrophobic block of the water pore.

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Gorgoni, Barbara, Yun-Bo Zhao, J. Krishnan, and Ian Stansfield. "Destabilization of Eukaryote mRNAs by 5′ Proximal Stop Codons Can Occur Independently of the Nonsense-Mediated mRNA Decay Pathway." Cells 8, no. 8 (July 31, 2019): 800. http://dx.doi.org/10.3390/cells8080800.

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In eukaryotes, the binding of poly(A) binding protein (PAB) to the poly(A) tail is central to maintaining mRNA stability. PABP interacts with the translation termination apparatus, and with eIF4G to maintain 3′–5′ mRNA interactions as part of an mRNA closed loop. It is however unclear how ribosome recycling on a closed loop mRNA is influenced by the proximity of the stop codon to the poly(A) tail, and how post-termination ribosome recycling affects mRNA stability. We show that in a yeast disabled for nonsense mediated mRNA decay (NMD), a PGK1 mRNA with an early stop codon at codon 22 of the reading frame is still highly unstable, and that this instability cannot be significantly countered even when 50% stop codon readthrough is triggered. In an NMD-deficient mutant yeast, stable reporter alleles with more 3′ proximal stop codons could not be rendered unstable through Rli1-depletion, inferring defective Rli1 ribosome recycling is insufficient in itself to trigger mRNA instability. Mathematical modelling of a translation system including the effect of ribosome recycling and poly(A) tail shortening supports the hypothesis that impaired ribosome recycling from 5′ proximal stop codons may compromise initiation processes and thus destabilize the mRNA. A model is proposed wherein ribosomes undergo a maturation process during early elongation steps, and acquire competency to re-initiate on the same mRNA as translation elongation progresses beyond the very 5′ proximal regions of the mRNA.

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Vohra, Shabana, Bruck Taddese, Alex C. Conner, David R. Poyner, Debbie L. Hay, James Barwell, Philip J. Reeves, Graham J. G. Upton, and Christopher A. Reynolds. "Similarity between class A and class B G-protein-coupled receptors exemplified through calcitonin gene-related peptide receptor modelling and mutagenesis studies." Journal of The Royal Society Interface 10, no. 79 (February 6, 2013): 20120846. http://dx.doi.org/10.1098/rsif.2012.0846.

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Modelling class B G-protein-coupled receptors (GPCRs) using class A GPCR structural templates is difficult due to lack of homology. The plant GPCR, GCR1, has homology to both class A and class B GPCRs. We have used this to generate a class A–class B alignment, and by incorporating maximum lagged correlation of entropy and hydrophobicity into a consensus score, we have been able to align receptor transmembrane regions. We have applied this analysis to generate active and inactive homology models of the class B calcitonin gene-related peptide (CGRP) receptor, and have supported it with site-directed mutagenesis data using 122 CGRP receptor residues and 144 published mutagenesis results on other class B GPCRs. The variation of sequence variability with structure, the analysis of polarity violations, the alignment of group-conserved residues and the mutagenesis results at 27 key positions were particularly informative in distinguishing between the proposed and plausible alternative alignments. Furthermore, we have been able to associate the key molecular features of the class B GPCR signalling machinery with their class A counterparts for the first time. These include the [K/R]KLH motif in intracellular loop 1, [I/L]xxxL and KxxK at the intracellular end of TM5 and TM6, the NPXXY/VAVLY motif on TM7 and small group-conserved residues in TM1, TM2, TM3 and TM7. The equivalent of the class A DRY motif is proposed to involve Arg 2.39 , His 2.43 and Glu 3.46 , which makes a polar lock with T 6.37 . These alignments and models provide useful tools for understanding class B GPCR function.

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Jeyakanthan, Jeyaraman, Shankar Prasad Kanaujia, Yuya Nishida, Noriko Nakagawa, Surendran Praveen, Akeo Shinkai, Seiki Kuramitsu, Shigeyuki Yokoyama, and Kanagaraj Sekar. "Free and ATP-bound structures of Ap4A hydrolase fromAquifex aeolicusV5." Acta Crystallographica Section D Biological Crystallography 66, no. 2 (January 22, 2010): 116–24. http://dx.doi.org/10.1107/s0907444909047064.

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Asymmetric diadenosine tetraphosphate (Ap4A) hydrolases degrade the metabolite Ap4A back into ATP and AMP. The three-dimensional crystal structure of Ap4A hydrolase (16 kDa) fromAquifex aeolicushas been determined in free and ATP-bound forms at 1.8 and 1.95 Å resolution, respectively. The overall three-dimensional crystal structure of the enzyme shows an αβα-sandwich architecture with a characteristic loop adjacent to the catalytic site of the protein molecule. The ATP molecule is bound in the primary active site and the adenine moiety of the nucleotide binds in a ring-stacking arrangement equivalent to that observed in the X-ray structure of Ap4A hydrolase fromCaenorhabditis elegans. Binding of ATP in the active site induces local conformational changes which may have important implications in the mechanism of substrate recognition in this class of enzymes. Furthermore, two invariant water molecules have been identified and their possible structural and/or functional roles are discussed. In addition, modelling of the substrate molecule at the primary active site of the enzyme suggests a possible path for entry and/or exit of the substrate and/or product molecule.

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Rao, Francesco V., Alexander W. Schüttelkopf, Helge C. Dorfmueller, Andrew T. Ferenbach, Iva Navratilova, and Daan M. F. van Aalten. "Structure of a bacterial putative acetyltransferase defines the fold of the human O -GlcNAcase C-terminal domain." Open Biology 3, no. 10 (October 2013): 130021. http://dx.doi.org/10.1098/rsob.130021.

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The dynamic modification of proteins by O -linked N -acetylglucosamine ( O -GlcNAc) is an essential posttranslational modification present in higher eukaryotes. Removal of O -GlcNAc is catalysed by O -GlcNAcase, a multi-domain enzyme that has been reported to be bifunctional, possessing both glycoside hydrolase and histone acetyltransferase (AT) activity. Insights into the mechanism, protein substrate recognition and inhibition of the hydrolase domain of human OGA (hOGA) have been obtained via the use of the structures of bacterial homologues. However, the molecular basis of AT activity of OGA, which has only been reported in vitro , is not presently understood. Here, we describe the crystal structure of a putative acetyltransferase ( Og pAT) that we identified in the genome of the marine bacterium Oceanicola granulosus , showing homology to the hOGA C-terminal AT domain (hOGA-AT) . The structure of Og pAT in complex with acetyl coenzyme A (AcCoA) reveals that, by homology modelling, hOGA-AT adopts a variant AT fold with a unique loop creating a deep tunnel. The structures, together with mutagenesis and surface plasmon resonance data, reveal that while the bacterial Og pAT binds AcCoA, the hOGA-AT does not, as explained by the lack of key residues normally required to bind AcCoA. Thus, the C-terminal domain of hOGA is a catalytically incompetent ‘pseudo’-AT.

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Rodrigues-Amorim, Daniela, Marta Iglesias-Martínez-Almeida, Tania Rivera-Baltanás, Patricia Fernández-Palleiro, Luis Freiría-Martínez, Cynthia Rodríguez-Jamardo, María Comís-Tuche, et al. "The Role of the Second Extracellular Loop of Norepinephrine Transporter, Neurotrophin-3 and Tropomyosin Receptor Kinase C in T Cells: A Peripheral Biomarker in the Etiology of Schizophrenia." International Journal of Molecular Sciences 22, no. 16 (August 7, 2021): 8499. http://dx.doi.org/10.3390/ijms22168499.

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The neurobiology of schizophrenia is multifactorial, comprising the dysregulation of several biochemical pathways and molecules. This research proposes a peripheral biomarker for schizophrenia that involves the second extracellular loop of norepinephrine transporter (NEText), the tropomyosin receptor kinase C (TrkC), and the neurotrophin-3 (NT-3) in T cells. The study of NEText, NT-3, and TrkC was performed in T cells and plasma extracted from peripheral blood of 54 patients with schizophrenia and 54 healthy controls. Levels of NT-3, TrkC, and NET were significantly lower in plasma and T cells of patients compared to healthy controls. Co-immunoprecipitation (co-IPs) showed protein interactions with Co-IP NEText–NT-3 and Co-IP NEText–TrkC. Computational modelling of protein–peptide docking by CABS-dock provided a medium–high accuracy model for NT-3–NEText (4.6935 Å) and TrkC–NEText (2.1365 Å). In summary, immunocomplexes reached statistical relevance in the T cells of the control group contrary to the results obtained with schizophrenia. The reduced expression of NT-3, TrkC, and NET, and the lack of molecular complexes in T cells of patients with schizophrenia may lead to a peripheral dysregulation of intracellular signaling pathways and an abnormal reuptake of norepinephrine (NE) by NET. This peripheral molecular biomarker underlying schizophrenia reinforces the role of neurotrophins, and noradrenergic and immune systems in the pathophysiology of schizophrenia.

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Das, Chinmaya Kumar, Umasankar Nayak, Preetinanda Pati, Mihir Ranjan Mohanty, Sujata Das, Parshuram Sial, Bhagban Kabat, and S. C. Swain. "Deciphering the Molecular Architecture of a Candidate R-gene (BjuWRR1) Product Mediating White Rust Resistance in Brassica juncea." International Journal of Bio-resource and Stress Management 12, no. 5 (August 31, 2021): 393–401. http://dx.doi.org/10.23910/1.2021.2205a.

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In this investigation, a three-dimensional model of a R-gene encoded product BjuWRR1 which is known to play a role in white rust resistance in Brassica juncea was developed to synthesize innovative ways for evolving white rust resistant cultivars. The model was built from the amino acid sequence of BjuWRR1 using structural template information of a disease resistance protein (RPP13-like protein 4 of Arabidopsis thaliana) with the help of homology-based modelling approach. Built models were validated for their stereochemical parameters and structural descriptors using Ramachandran plot analysis, protein structure analysis and ERRAT analysis. Structural analysis of BjuWRR1 model revealed that it is composed of three distinct domains namely a coiled-coil domain, a central NB-ARC nucleotide binding domain and a hypervariable leucine-rich repeat domain. Further, canonical conserved motifs such as P-loop, Kinase2-motif and HD-motif were found in the NB-ARC domain. The built model would help in understanding the molecular basis of plant-immunity against white rust pathogen by understanding the significance of inter-domain interactions in BuWRR1 in triggering the activation of downstream defense response against the white rust pathogen by promoting oligomerization of coiled-coil domains through stabilized hydrophobic interactions and interaction with NB-ARC domain. Presence of patches of charged residues in each domain of BjuWRR1 indicated their possible role in intra-molecular interaction with other domains. Therefore, this model can help in designing functional genomic studies to understand the role of intra-molecular interaction in BjuWRR1 to mediate resistance against white rust pathogen.

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Journal articles on the topic 'Protein loop modelling'

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