Publications

2013

• Endosomal WASH and exocyst complexes control exocytosis of MT1-MMP at invadopodia
  
  • Monteiro Pedro
  • Rossé Carine
  • Castro-Castro Antonio
  • Irondelle Marie
  • Lagoutte Emilie
  • Paul-Gilloteaux Perrine
  • Desnos Claire
  • Formstecher Etienne
  • Darchen François
  • Perrais David
  • Gautreau Alexis
  • Hertzog Maud
  • Chavrier Philippe
  Journal of Cell Biology, Rockefeller University Press, 2013, 203 (6), pp.1063 - 1079. Remodeling of the extracellular matrix by carcinoma cells during metastatic dissemination requires formation of actin-based protrusions of the plasma membrane called invadopodia, where the trans-membrane type 1 matrix metalloproteinase (MT1-MMP) accumulates. Here, we describe an interaction between the exocyst complex and the endosomal Arp2/3 activator Wiskott-Aldrich syndrome protein and Scar homolog (WASH) on MT1-MMP–containing late endosomes in invasive breast carcinoma cells. We found that WASH and exocyst are required for matrix degradation by an exocytic mechanism that involves tubular connections between MT1-MMP–positive late endosomes and the plasma membrane in contact with the matrix. This ensures focal delivery of MT1-MMP and supports pericellular matrix degradation and tumor cell invasion into different pathologically relevant matrix environments. Our data suggest a general mechanism used by tumor cells to breach the basement membrane and for invasive migration through fibrous collagen-enriched tissues surrounding the tumor. (10.1083/jcb.201306162)
  DOI : 10.1083/jcb.201306162
• Monte Carlo simulations of proteins at constant pH with generalized Born solvent, flexible sidechains, and an effective dielectric boundary.
  
  • Polydorides Savvas
  • Simonson Thomas
  Journal of Computational Chemistry, Wiley, 2013, 34 (31), pp.2742-2756. Titratable residues determine the acid/base behavior of proteins, strongly influencing their function; in addition, proton binding is a valuable reporter on electrostatic interactions. We describe a method for pK(a) calculations, using constant-pH Monte Carlo (MC) simulations to explore the space of sidechain conformations and protonation states, with an efficient and accurate generalized Born model (GB) for the solvent effects. To overcome the many-body dependency of the GB model, we use a "Native Environment" approximation, whose accuracy is shown to be good. It allows the precalculation and storage of interactions between all sidechain pairs, a strategy borrowed from computational protein design, which makes the MC simulations themselves very fast. The method is tested for 12 proteins and 167 titratable sidechains. It gives an rms error of 1.1 pH units, similar to the trivial "Null" model. The only adjustable parameter is the protein dielectric constant. The best accuracy is achieved for values between 4 and 8, a range that is physically plausible for a protein interior. For sidechains with large pKa shifts, ≥2, the rms error is 1.6, compared to 2.5 with the Null model and 1.5 with the empirical PROPKA method. (10.1002/jcc.23450)
  DOI : 10.1002/jcc.23450
• Identification of the Rps28 binding motif from yeast Edc3 involved in the autoregulatory feedback loop controlling RPS28B mRNA decay.
  
  • Kolesnikova Olga
  • Back Régis
  • Graille Marc
  • Séraphin Bertrand
  Nucleic Acids Research, Oxford University Press, 2013, 41 (20), pp.9514-9523. In the yeast Saccharomyces cerevisiae, the Edc3 protein was previously reported to participate in the auto-regulatory feedback loop controlling the level of the RPS28B messenger RNA (mRNA). We show here that Edc3 binds directly and tightly to the globular core of Rps28 ribosomal protein. This binding occurs through a motif that is present exclusively in Edc3 proteins from yeast belonging to the Saccharomycetaceae phylum. Functional analyses indicate that the ability of Edc3 to interact with Rps28 is not required for its general function and for its role in the regulation of the YRA1 pre-mRNA decay. In contrast, this interaction appears to be exclusively required for the auto-regulatory mechanism controlling the RPS28B mRNA decay. These observations suggest a plausible model for the evolutionary appearance of a Rps28 binding motif in Edc3. (10.1093/nar/gkt607)
  DOI : 10.1093/nar/gkt607
• Computational protein design: The proteus software and selected applications.
  
  • Simonson Thomas
  • Gaillard Thomas
  • Mignon David
  • Schmidt Am Busch Marcel
  • Lopes Anne
  • Amara Najette
  • Polydorides Savvas
  • Sedano Audrey
  • Druart Karen
  • Archontis Georgios
  Journal of Computational Chemistry, Wiley, 2013, 34 (28), pp.2472-84. We describe an automated procedure for protein design, implemented in a flexible software package, called Proteus. System setup and calculation of an energy matrix are done with the XPLOR modeling program and its sophisticated command language, supporting several force fields and solvent models. A second program provides algorithms to search sequence space. It allows a decomposition of the system into groups, which can be combined in different ways in the energy function, for both positive and negative design. The whole procedure can be controlled by editing 2-4 scripts. Two applications consider the tyrosyl-tRNA synthetase enzyme and its successful redesign to bind both O-methyl-tyrosine and D-tyrosine. For the latter, we present Monte Carlo simulations where the D-tyrosine concentration is gradually increased, displacing L-tyrosine from the binding pocket and yielding the binding free energy difference, in good agreement with experiment. Complete redesign of the Crk SH3 domain is presented. The top 10000 sequences are all assigned to the correct fold by the SUPERFAMILY library of Hidden Markov Models. Finally, we report the acid/base behavior of the SNase protein. Sidechain protonation is treated as a form of mutation; it is then straightforward to perform constant-pH Monte Carlo simulations, which yield good agreement with experiment. Overall, the software can be used for a wide range of application, producing not only native-like sequences but also thermodynamic properties with errors that appear comparable to other current software packages.Copyright © 2013 Wiley Periodicals, Inc. (10.1002/jcc.23418)
  DOI : 10.1002/jcc.23418
• What Is the Dielectric Constant of a Protein When Its Backbone Is Fixed?
  
  • Simonson Thomas
  Journal of Chemical Theory and Computation, American Chemical Society, 2013, 9 (10), pp.4603-4608. Monte Carlo (MC) simulations with a fixed protein backbone but mobile sidechains are common for acid/base constants and protein design. To characterize the fluctuations in these models, estimating the Frohlich-Kirkwood dielectric constant can give physical insight and allow comparison both with models that are more rigorous (fully flexible) and ones that are simpler (Poisson-Boltmann without any explicit protein flexibility). MC simulations of two small proteins yield protein dielectric constants of 12 and 14, about 70% of the result from MD (16 and 22). Thus, the consistency between the fully explicit MD and partly explicit MC is only fair. (10.1021/ct400398e)
  DOI : 10.1021/ct400398e
• Mechanism of activation of elongation factor Tu by ribosome: Catalytic histidine activates GTP by protonation.
  
  • Aleksandrov Alexey
  • Field Martin J
  RNA, Cold Spring Harbor Laboratory Press, 2013, 19 (9), pp.1218-25. Elongation factor Tu (EF-Tu) is central to prokaryotic protein synthesis as it has the role of delivering amino-acylated tRNAs to the ribosome. Release of EF-Tu, after correct binding of the EF-Tu:aa-tRNA complex to the ribosome, is initiated by GTP hydrolysis. This reaction, whose mechanism is uncertain, is catalyzed by EF-Tu, but requires activation by the ribosome. There have been a number of mechanistic proposals, including those spurred by a recent X-ray crystallographic analysis of a ribosome:EF-Tu:aa-tRNA:GTP-analog complex. In this work, we have investigated these and alternative hypotheses, using high-level quantum chemical/molecular mechanical simulations for the wild-type protein and its His85Gln mutant. For both proteins, we find previously unsuggested mechanisms as being preferred, in which residue 85, either His or Gln, directly assists in the reaction. Analysis shows that the RNA has a minor catalytic effect in the wild-type reaction, but plays a significant role in the mutant by greatly stabilizing the reaction's transition state. Given the similarity between EF-Tu and other members of the translational G-protein family, it is likely that these mechanisms of ribosome-activated GTP hydrolysis are pertinent to all of these proteins. (10.1261/rna.040097.113)
  DOI : 10.1261/rna.040097.113
• Design computationnel de protéines pour la prédiction de structure
  
  • Sedano-Pelzer Audrey
  , 2013. Grâce aux récents progrès technologiques et à l'arrivée des séquenceurs de nouvelle génération, la quantité de données génomiques croît exponentiellement, alors que l'écart avec le nombre de structures résolues se creuse. Dans l'idéal, on aimerait pouvoir prédire par informatique la structure 3D de n'importe quelle protéine à partir de l'information de séquence seule, même en l'absence d'homologie. En effet, en dessous de 30% d'identité de séquence, les mesures de similarité de séquences ne sont plus suffisantes pour détecter l'homologie. Il faut donc mettre en place d'autres méthodes afin de venir à bout de cette zone d'ombre. Pour une structure donnée (et donc une fonction biologique), on ne dispose souvent que d'une petite quantité de séquences natives y correspondant, et parfois assez peu identiques. Il est alors difficile de construire un profil de recherche d'homologues pour retrouver ces séquences dont on ne connaîtrait pas la structure. Alors comment disposer de bases de données de séquences plus conséquentes pour chaque structure ? Ainsi, le design computationnel de protéine (CPD) tente de répondre à cette problématique : si l'on connaît un repliement, est-il possible de retrouver l'ensemble des séquences qui lui correspondent ? Le principe du CPD consiste à identifier parmi toutes les séquences compatibles avec le repliement d'intérêt, celles qui vont conférer à la protéine, la fonction désirée. La procédure générale est réalisée en deux étapes. La première consiste à calculer une matrice d'énergie contenant les énergies d'interactions entre toutes les paires de résidus de la protéine en autorisant successivement tous les types d'acides aminés dans toutes leurs conformations possibles. La seconde étape, ou "phase d'optimisation", consiste à explorer simultanément l'espace des séquences et des conformations afin de déterminer la combinaison optimale d'acides aminés étant donné le repliement de départ. Une première phase d'analyse de covariances de positions d'alignements de séquences théoriques a été menée. Nous avons ainsi pu mettre au point une méthode statistique pour repérer des ensembles de positions qui muteraient ensemble pour une structure donnée. La construction d'un profil avec toutes ces séquences théoriques moyennant trop l'information en acides aminés, nous avons pu améliorer la recherche d'homologues en construisant plusieurs profils à partir de groupes de séquences classées grâce à des motifs sur ces positions considérées comme covariantes. Pour mieux appréhender la qualité de ces prédictions de séquences théoriques, il fallait mettre en place un protocole de sélection des meilleurs protéines mutantes afin de les tester in vivo. Mais comment déterminer qu'une séquence théorique est meilleure qu'une autre? Sur quels critères se baser pour les caractériser? Aussi, un ensemble de descripteurs a été choisi, permettant de trier sur plusieurs critères les séquences théoriques pour n'en choisir qu'une vingtaine. Ensuite, ces protéines mutantes ont été soumises à des simulations de dynamique moléculaire afin d'évaluer leur stabilité théorique. Pour quelques protéines mutantes plus prometteuses, nous avons réalisé des expériences de sur-expression, de purification et de détermination structurale, tentant d'obtenir une validation biologique du modèle de CPD. Ces protocoles d'analyse et de validation semblent être de bons moyens permettront à notre équipe de tester d'autres protéines mutantes dans l'avenir. Ils pourront ainsi modifier des paramètres lors de la génération par CPD et s'appuyer sur des résultats expérimentaux pour les ajuster.
• Protein: ligand recognition: simple models for electrostatic effects.
  
  • Simonson Thomas
  Current Pharmaceutical Design, Bentham Science Publishers, 2013, 19 (23), pp.4241-4256. Free energy simulations are a powerful tool to study molecular recognition. The most rigorous variants can provide in depth understanding for a particular system, but are not suited for high throughput application to large libraries of compounds. Related, but less expensive methods are increasingly popular, including continuum electrostatic methods like PBSA (''Poisson-Boltzmann Surface Area'') and Linear Response or Linear Interaction Energy methods (LRA, LIE). Here, we review the theoretical background of these methods and provide a unified framework. We focus on the electrostatic contributions to the binding free energy, analyzing nonpolar contributions more briefly. The methods reviewed introduce a multi-step pathway for ligand unbinding, with distinct steps that uncharge the bound ligand, then recharge the unbound ligand. They assume that the system responds to the charging/uncharging in a linear way. With this approximation, the free energy can be described by its one or two first derivatives with respect to a progress variable. The methods can then be classified according to which states of the system are actually simulated and the number of free energy derivatives (one or two) that are employed. The analysis should help clarify the relations between several important free energy methods and the approximations they make. It can suggest new ways to test them, and provide routes for their improvement.
• Crystal structure of PAV1-137: a protein from the virus PAV1 that infects Pyrococcus abyssi.
  
  • Leulliot N.
  • Quevillon-Cheruel S.
  • Graille M.
  • Geslin C.
  • Flament D.
  • Le Romancer M.
  • van Tilbeurgh H.
  Archaea, Hindawi Publishing Corporation, 2013, 2013, pp.568053. Pyrococcus abyssi virus 1 (PAV1) was the first virus particle infecting a hyperthermophilic Euryarchaeota (Pyrococcus abyssi strain GE23) that has been isolated and characterized. It is lemon shaped and is decorated with a short fibered tail. PAV1 morphologically resembles the fusiform members of the family Fuselloviridae or the genus Salterprovirus. The 18 kb dsDNA genome of PAV1 contains 25 predicted genes, most of them of unknown function. To help assigning functions to these proteins, we have initiated structural studies of the PAV1 proteome. We determined the crystal structure of a putative protein of 137 residues (PAV1-137) at a resolution of 2.2 Å. The protein forms dimers both in solution and in the crystal. The fold of PAV1-137 is a four- α -helical bundle analogous to those found in some eukaryotic adhesion proteins such as focal adhesion kinase, suggesting that PAV1-137 is involved in protein-protein interactions. (10.1155/2013/568053)
  DOI : 10.1155/2013/568053
• Simulating GTP:Mg and GDP:Mg with a simple force field: A structural and thermodynamic analysis
  
  • Simonson Thomas
  • Satpati Priyadarshi
  Journal of Computational Chemistry, Wiley, 2013, 34 (10), pp.836-846. Di- and tri-phosphate nucleotides are essential cofactors for many proteins, usually in an Mg(2+) -bound form. Proteins like GTPases often detect the difference between NDP and NTP and respond by changing conformations. To study such complexes, simple, fixed charge force fields have been used, which allow long simulations and precise free energy calculations. The preference for NTP or NDP binding depends on many factors, including ligand structure and Mg(2+) coordination and the changes they undergo upon binding. Here, we use a simple force field to examine two Mg(2+) coordination modes for the unbound GDP and GTP: direct, or "Inner Sphere" (IS) coordination by one or more phosphate oxygens and indirect, "Outer Sphere" (OS) coordination involving one or more bridging waters. We compare GTP: and GDP:Mg binding with OS and IS coordination; combining the results with experimental data then indicates that GTP prefers the latter. We also examine different kinds of IS coordination and their sensitivity to a key force field parameter: the optimal Mg:oxygen van der Waals distance Rmin . Increasing Rmin improves the Mg:oxygen distances, the GTP: and GDP:Mg binding affinities, and the fraction of GTP:Mg with β + γ phosphate coordination, but does not improve or change the GTP/GDP affinity difference, which remains much larger than experiment. It has no effect on the free energy of GDP binding to a GTPase. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc. (10.1002/jcc.23207)
  DOI : 10.1002/jcc.23207
• Neutralization by Metal Ions of the Toxicity of Sodium Selenide
  
  • Dauplais Marc
  • Lazard Myriam
  • Blanquet Sylvain
  • Plateau Pierre
  PLoS ONE, Public Library of Science, 2013, 8 (1), pp.e54353. Inert metal-selenide colloids are found in animals. They are believed to afford cross-protection against the toxicities of both metals and selenocompounds. Here, the toxicities of metal salt and sodium selenide mixtures were systematically studied using the death rate of Saccharomyces cerevisiae cells as an indicator. In parallel, the abilities of these mixtures to produce colloids were assessed. Studied metal cations could be classified in three groups: (i) metal ions that protect cells against selenium toxicity and form insoluble colloids with selenide (Ag+, Cd2+, Cu2+, Hg2+, Pb2+ and Zn2+), (ii) metal ions which protect cells by producing insoluble metal-selenide complexes and by catalyzing hydrogen selenide oxidation in the presence of dioxygen (Co2+ and Ni2+) and, finally, (iii) metal ions which do not afford protection and do not interact (Ca2+, Mg2+, Mn2+) or weakly interact (Fe2+) with selenide under the assayed conditions. When occurring, the insoluble complexes formed from divalent metal ions and selenide contained equimolar amounts of metal and selenium atoms. With the monovalent silver ion, the complex contained two silver atoms per selenium atom. Next, because selenides are compounds prone to oxidation, the stabilities of the above colloids were evaluated under oxidizing conditions. 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), the reduction of which can be optically followed, was used to promote selenide oxidation. Complexes with cadmium, copper, lead, mercury or silver resisted dissolution by DTNB treatment over several hours. With nickel and cobalt, partial oxidation by DTNB occurred. On the other hand, when starting from ZnSe or FeSe complexes, full decompositions were obtained within a few tens of minutes. The above properties possibly explain why ZnSe and FeSe nanoparticles were not detected in animals exposed to selenocompounds. (10.1371/journal.pone.0054353)
  DOI : 10.1371/journal.pone.0054353
• Protein Structural Statistics with PSS
  
  • Gaillard Thomas
  • Schwarz Benjamin
  • Chebaro Yasmine
  • Stote Roland H
  • Dejaegere Annick
  Journal of Chemical Information and Modeling, American Chemical Society, 2013, 53 (9), pp.2471-2482. Characterizing the variability within an ensemble of protein structures is a common requirement in structural biology and bioinformatics. With the increasing number of protein structures becoming available, there is a need for new tools capable of automating the structural comparison of large ensemble of structures. We present Protein Structural Statistics (PSS), a command-line program written in Perl for Unix-like environments, dedicated to the calculation of structural statistics for a set of proteins. PSS can perform multiple sequence alignments, structure superpositions, calculate Cartesian and dihedral coordinate statistics, and execute cluster analyses. An HTML report that contains a convenient summary of results with figures, tables, and hyperlinks can also be produced. PSS is a new tool providing an automated way to compare multiple structures. It integrates various types of structural analyses through an user-friendly and flexible interface, facilitating the access to powerful but more specialized programs. PSS is easy to modify and extend and is distributed under a free and open source license. The relevance of PSS is illustrated by examples of application to pertinent biological problems. (10.1021/ci400233j)
  DOI : 10.1021/ci400233j
• Capturing the mutational landscape of the beta-lactamase TEM-1
  
  • Jacquier Hervé
  • Birgy André
  • Le Nagard Hervé
  • Mechulam Yves
  • Schmitt Emmanuelle
  • Glodt Jérémy
  • Bercot Béatrice
  • Petit Emmanuelle
  • Poulain Julie
  • Barnaud Guilène
  • Gros Pierre-Alexis
  • Tenaillon Olivier
  Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences, 2013, 110 (32), pp.13067-13072. Adaptation proceeds through the selection of mutations. The distribution of mutant fitness effect and the forces shaping this distribution are therefore keys to predict the evolutionary fate of organisms and their constituents such as enzymes. Here, by producing and sequencing a comprehensive collection of 10,000 mutants, we explore the mutational landscape of one enzyme involved in the spread of antibiotic resistance, the beta-lactamase TEM-1. We measured mutation impact on the enzyme activity through the estimation of amoxicillin minimum inhibitory concentration on a subset of 990 mutants carrying a unique missense mutation, representing 64% of possible amino acid changes in that protein reachable by point mutation. We established that mutation type, solvent accessibility of residues, and the predicted effect of mutations on protein stability primarily determined alone or in combination changes in minimum inhibitory concentration of mutants. Moreover, we were able to capture the drastic modification of the mutational landscape induced by a single stabilizing point mutation (M182T) by a simple model of protein stability. This work thereby provides an integrated framework to study mutation effects and a tool to understand/define better the epistatic interactions. (10.1073/pnas.1215206110)
  DOI : 10.1073/pnas.1215206110
• Roles of yeast eIF2α and eIF2β subunits in the binding of the initiator methionyl-tRNA
  
  • Naveau Marie
  • Lazennec-Schurdevin Christine
  • Panvert Michel
  • Dubiez Etienne
  • Mechulam Yves
  • Schmitt Emmanuelle
  Nucleic Acids Research, Oxford University Press, 2013, 41 (1), pp.1047-1057. Heterotrimeric eukaryotic/archaeal translation initiation factor 2 (e/aIF2) binds initiator methionyl-tRNA and plays a key role in the selection of the start codon on messenger RNA. tRNA binding was extensively studied in the archaeal system. The γ subunit is able to bind tRNA, but the α subunit is required to reach high affinity whereas the β subunit has only a minor role. In Saccharomyces cerevisiae however, the available data suggest an opposite scenario with β having the most important contribution to tRNA-binding affinity. In order to overcome difficulties with purification of the yeast eIF2γ subunit, we designed chimeric eIF2 by assembling yeast α and β subunits to archaeal γ subunit. We show that the β subunit of yeast has indeed an important role, with the eukaryote-specific N- and C-terminal domains being necessary to obtain full tRNA-binding affinity. The α subunit apparently has a modest contribution. However, the positive effect of α on tRNA binding can be progressively increased upon shortening the acidic C-terminal extension. These results, together with small angle X-ray scattering experiments, support the idea that in yeast eIF2, the tRNA molecule is bound by the α subunit in a manner similar to that observed in the archaeal aIF2-GDPNP-tRNA complex. © The Author(s) 2012. Published by Oxford University Press. (10.1093/nar/gks1180)
  DOI : 10.1093/nar/gks1180