Publications

2010

• Cartographie structurale et fonctionnelle de la liaison entre la peptidyl-ARNt hydrolase et son substrat
  
  • Laurent Giorgi
  , 2010. La peptidyl-ARNt hydrolase est une enzyme qui hydrolyse les peptidyl-ARNt issus d'une terminaison prématurée de la traduction. Cette protéine est essentielle à la viabilité des bactéries, mais pas à celle des eucaryotes, ce qui fait d'elle une cible potentielle pour l'action d'anti-bactériens. Cela justifie également qu'on cherche à cartographier l'interaction de cette protéine avec son substrat, pour faciliter la conception d'inhibiteur. Les tentatives d'obtention de cristaux de complexes enzyme:analogue de substrat étant restées vaines, nous avons choisi d'étudier de tels complexes en solution, par RMN. Grâce à un double marquage 15N/13C, nous avons tout d'abord attribué les fréquences de résonance des atomes du squelette de la protéine et d'une grande partie des chaînes latérale. Nous avons ensuite étudié l'interaction entre la PTH d'E. coli et un analogue de son substrat synthétisé chimiquement, la diacétyl-Lys-(3'NH)-adénosine. Cette étude nous a permis de caractériser le rôle de nombreux résidus du site actif, notamment celui d'une phénylalanine (F66) interagissant via son cycle aromatique avec l'adénine 3'-terminale du substrat, celui d'une asparagine (N114) stabilisant une molécule d'eau responsable de l'hydrolyse du substrat et celui d'une autre asparagine (N10) permettant à la PTH de discriminer positivement les peptidyl-ARNt par rapport aux aminoacyl-ARNt. Nous avons aussi étudié l'interaction entre la protéine et des mini-ARNt mimant la tige acceptrice et le bras TΨC d'un ARNt. Ce travail a permis de cartographier la surface de la PTH où l'ARN s'ancre à la protéine. Il a confirmé l'importance de deux résidus basiques, la lysine K105 et l'arginine R133, pour la reconnaissance du phosphate en 5' de l'ARNt. Il a également révélé une interaction entre l'hélice C-terminale de la protéine et le bras TΨC de l'ARNt, à 30 Å du site actif. La pertinence fonctionnelle de ce dernier contact a pu être établie par mutagenèse dirigée. L'ensemble de ces résultats permet de proposer un modèle complet de l'interaction entre la PTH et un peptidyl-ARNt.
• Uptake of selenite by Saccharomyces cerevisiae involves the high and low affinity orthophosphate transporters.
  
  • Lazard Myriam
  • Blanquet Sylvain
  • Fisicaro Paola
  • Labarraque Guillaume
  • Plateau Pierre
  Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2010, 285 (42), pp.32029-37. Although the general cytotoxicity of selenite is well established, the mechanism by which this compound crosses cellular membranes is still unknown. Here, we show that in Saccharomyces cerevisiae, the transport system used opportunistically by selenite depends on the phosphate concentration in the growth medium. Both the high and low affinity phosphate transporters are involved in selenite uptake. When cells are grown at low P(i) concentrations, the high affinity phosphate transporter Pho84p is the major contributor to selenite uptake. When phosphate is abundant, selenite is internalized through the low affinity P(i) transporters (Pho87p, Pho90p, and Pho91p). Accordingly, inactivation of the high affinity phosphate transporter Pho84p results in increased resistance to selenite and reduced uptake in low P(i) medium, whereas deletion of SPL2, a negative regulator of low affinity phosphate uptake, results in exacerbated sensitivity to selenite. Measurements of the kinetic parameters for selenite and phosphate uptake demonstrate that there is a competition between phosphate and selenite ions for both P(i) transport systems. In addition, our results indicate that Pho84p is very selective for phosphate as compared with selenite, whereas the low affinity transporters discriminate less efficiently between the two ions. The properties of phosphate and selenite transport enable us to propose an explanation to the paradoxical increase of selenite toxicity when phosphate concentration in the growth medium is raised above 1 mm. (10.1074/jbc.M110.139865)
  DOI : 10.1074/jbc.M110.139865
• tRNA binding properties of eukaryotic translation initiation factor 2 from Encephalitozoon cuniculi.
  
  • Naveau Marie
  • Lazennec-Schurdevin Christine
  • Panvert Michel
  • Mechulam Yves
  • Schmitt Emmanuelle
  Biochemistry, American Chemical Society, 2010, 49 (40), pp.8680-8. A critical consequence of the initiation of translation is the setting of the reading frame for mRNA decoding. In eukaryotic and archaeal cells, heterotrimeric initiation factor e/aIF2, in its GTP form, specifically binds Met-tRNA(i)(Met) throughout the translation initiation process. After start codon recognition, the factor, in its GDP-bound form, loses affinity for Met-tRNA(i)(Met) and eventually dissociates from the initiation complex. The role of each aIF2 subunit in tRNA binding has been extensively studied in archaeal systems. The isolated archaeal γ subunit is able to bind tRNA, but the α subunit is required for strong binding. Until now, difficulties during purification have hampered the study of the role of each of the three subunits of eukaryotic eIF2 in specific binding of the initiator tRNA. Here, we have produced the three subunits of eIF2 from Encephalitozoon cuniculi, isolated or assembled into heterodimers or into the full heterotrimer. Using assays following protection of Met-tRNA(i)(Met) against deacylation, we show that the eukaryotic γ subunit is able to bind by itself the initiator tRNA. However, the two peripheral α and β subunits are required for strong binding and contribute equally to tRNA binding affinity. The core domains of α and β probably act indirectly by stabilizing the tRNA binding site on the γ subunit. These results, together with those previously obtained with archaeal aIF2 and yeast eIF2, show species-specific distributions of the roles of the peripheral subunits of e/aIF2 in tRNA binding. (10.1021/bi1009166)
  DOI : 10.1021/bi1009166
• Predicting the acid/base behavior of proteins: a constant-pH Monte Carlo approach with generalized born solvent.
  
  • Aleksandrov Alexey
  • Polydorides Savvas
  • Archontis Georgios
  • Simonson Thomas
  Journal of Physical Chemistry B, American Chemical Society, 2010, 114 (32), pp.10634-48. The acid/base properties of proteins are essential in biochemistry, and proton binding is a valuable reporter on electrostatic interactions. We propose a constant-pH Monte Carlo strategy to compute protonation free energies and pK(a)'s. The solvent is described implicitly, through a generalized Born model. The electronic polarizability and backbone motions of the protein are included through the protein dielectric constant. Side chain motions are described explicitly, by the Monte Carlo scheme. An efficient computational algorithm is described, which allows us to treat the fluctuating shape of the protein/solvent boundary in a way that is numerically exact (within the GB framework); this contrasts with several previous constant-pH approaches. For a test set of six proteins and 78 titratable groups, the model performs well, with an rms error of 1.2 pH units. While this is slightly greater than a simple Null model (rms error of 1.1) and a fully empirical model (rms error of 0.9), it is obtained using physically meaningful model parameters, including a low protein dielectric of four. Importantly, similar performance is obtained for side chains with large and small pK(a) shifts (relative to a standard model compound). The titration curve slopes and the conformations sampled are reasonable. Several directions to improve the method further are discussed. (10.1021/jp104406x)
  DOI : 10.1021/jp104406x
• A brain-specific isoform of mitochondrial apoptosis-inducing factor: AIF2
  
  • Hangen E
  • de Zio D
  • Bordi M
  • Zhu C
  • Dessen P.
  • Caffin F
  • Lachkar S.
  • Perfettini J-L
  • Lazar V
  • Benard J.
  • Fimia G
  • Piacentini M.
  • Harper F
  • Pierron G
  • Vicencio J
  • Bénit P
  • de Andrade A
  • Höglinger G
  • Culmsee C
  • Rustin P.
  • Blomgren K
  • Cecconi F.
  • Kroemer G.
  • Modjtahedi Nazanine
  Cell Death and Differentiation, Nature Publishing Group, 2010, 17 (7), pp.1155-1166. (10.1038/cdd.2009.211)
  DOI : 10.1038/cdd.2009.211
• Mécanismes d'endommagement tribologiques du WC-6% CO en usinage
  
  • Kagnaya Tchadja
  • Boher Christine
  • Lambert Laurence
  • Lazard Myriam
  • Cutard Thierry
  , 2013, pp.p.355-360.
• 2D label-free imaging of resonant grating biochips in ultraviolet
  
  • Bougot-Robin Kristelle
  • Reverchon Jean-Luc
  • Fromant Michel
  • Mugherli Laurent
  • Plateau Pierre
  • Benisty Henri
  Optics Express, Optical Society of America - OSA Publishing, 2010, 8 (11), pp.11472. 2D images of label-free biochips exploiting resonant waveguide grating (RWG) are presented. They indicate sensitivities on the order of 1 pg/mm2 for proteins in air, and hence 10 pg/mm2 in water can be safely expected. A 320×256 pixels Aluminum-Gallium-Nitride-based sensor array is used, with an intrinsic narrow spectral window centered at 280 nm. The additional role of characteristic biological layer absorption at this wavelength is calculated, and regimes revealing its impact are discussed. Experimentally, the resonance of a chip coated with protein is revealed and the sensitivity evaluated through angular spectroscopy and imaging. In addition to a sensitivity similar to surface plasmon resonance (SPR), the RWGs resonance can be flexibly tailored to gain spatial, biochemical, or spectral sensitivity. (10.1364/OE.18.011472)
  DOI : 10.1364/OE.18.011472
• A molecular mechanics model for imatinib and imatinib:kinase binding.
  
  • Aleksandrov Alexey
  • Simonson Thomas
  Journal of Computational Chemistry, Wiley, 2010, 31 (7), pp.1550-60. Imatinib is an important anticancer drug, which binds specifically to the Abl kinase and blocks its signalling activity. To model imatinib:protein interactions, we have developed a molecular mechanics force field for imatinib and four close analogues, which is consistent with the CHARMM force field for proteins and nucleic acids. Atomic charges and Lennard-Jones parameters were derived from a supermolecule ab initio approach. We considered the ab initio energies and geometries of a probe water molecule interacting with imatinib fragments at 32 different positions. We considered both a neutral and a protonated imatinib. The final RMS deviation between the ab initio and force field energies, averaged over both forms, was 0.2 kcal/mol. The model also reproduces the ab initio geometry and flexibility of imatinib. To apply the force field to imatinib:Abl simulations, it is also necessary to determine the most likely imatinib protonation state when it binds to Abl. This was done using molecular dynamics free energy simulations, where imatinib is reversibly protonated during a series of MD simulations, both in solution and in complex with Abl. The simulations indicate that imatinib binds to Abl in its protonated, positively-charged form. To help test the force field and the protonation prediction, we did MD free energy simulations that compare the Abl binding affinities of two imatinib analogs, obtaining good agreement with experiment. Finally, two new imatinib variants were considered, one of which is predicted to have improved Abl binding. This variant could be of interest as a potential drug. (10.1002/jcc.21442)
  DOI : 10.1002/jcc.21442
• Molecular dynamics simulations show that conformational selection governs the binding preferences of imatinib for several tyrosine kinases.
  
  • Aleksandrov Alexey
  • Simonson Thomas
  Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2010, 285 (18), pp.13807-15. Tyrosine kinases transmit cellular signals through a complex mechanism, involving their phosphorylation and switching between inactive and active conformations. The cancer drug imatinib binds tightly to several homologous kinases, including Abl, but weakly to others, including Src. Imatinib specifically targets the inactive, so-called "DFG-out" conformation of Abl, which differs from the preferred, "DFG-in" conformation of Src in the orientation of a conserved Asp-Phe-Gly (DFG) activation loop. However, recent x-ray structures showed that Src can also adopt the DFG-out conformation and uses it to bind imatinib. The Src/Abl-binding free energy difference can thus be decomposed into two contributions. Contribution i measures the different protein-imatinib interactions when either kinase is in its DFG-out conformation. Contribution ii depends on the ability of imatinib to select or induce this conformation, i.e. on the relative stabilities of the DFG-out and DFG-in conformations of each kinase. Neither contribution has been measured experimentally. We use molecular dynamics simulations to show that contribution i is very small, 0.2 +/- 0.6 kcal/mol; imatinib interactions are very similar in the two kinases, including long range electrostatic interactions with the imatinib positive charge. Contribution ii, deduced using the experimental binding free energy difference, is much larger, 4.4 +/- 0.9 kcal/mol. Thus, conformational selection, easy in Abl, difficult in Src, underpins imatinib specificity. Contribution ii has a simple interpretation; it closely approximates the stability difference between the DFG-out and DFG-in conformations of apo-Src. Additional calculations show that conformational selection also governs the relative binding of imatinib to the kinases c-Kit and Lck. These results should help clarify the current framework for engineering kinase signaling. (10.1074/jbc.M110.109660)
  DOI : 10.1074/jbc.M110.109660
• Computational design of protein-ligand binding: modifying the specificity of asparaginyl-tRNA synthetase.
  
  • Lopes Anne
  • Schmidt Am Busch Marcel
  • Simonson Thomas
  Journal of Computational Chemistry, Wiley, 2010, 31 (6), pp.1273-86. A method for computational design of protein-ligand interactions is implemented and tested on the asparaginyl- and aspartyl-tRNA synthetase enzymes (AsnRS, AspRS). The substrate specificity of these enzymes is crucial for the accurate translation of the genetic code. The method relies on a molecular mechanics energy function and a simple, continuum electrostatic, implicit solvent model. As test calculations, we first compute AspRS-substrate binding free energy changes due to nine point mutations, for which experimental data are available; we also perform large-scale redesign of the entire active site of each enzyme (40 amino acids) and compare to experimental sequences. We then apply the method to engineer an increased binding of aspartyl-adenylate (AspAMP) into AsnRS. Mutants are obtained using several directed evolution protocols, where four or five amino acid positions in the active site are randomized. Promising mutants are subjected to molecular dynamics simulations; Poisson-Boltzmann calculations provide an estimate of the corresponding, AspAMP, binding free energy changes, relative to the native AsnRS. Several of the mutants are predicted to have an inverted binding specificity, preferring to bind AspAMP rather than the natural substrate, AsnAMP. The computed binding affinities are significantly weaker than the native, AsnRS:AsnAMP affinity, and in most cases, the active site structure is significantly changed, compared to the native complex. This almost certainly precludes catalytic activity. One of the designed sequences has a higher affinity and more native-like structure and may represent a valid candidate for Asp activity. (10.1002/jcc.21414)
  DOI : 10.1002/jcc.21414
• Nonantibiotic properties of tetracyclines: structural basis for inhibition of secretory phospholipase A2.
  
  • Dalm Daniela
  • Palm Gottfried J.
  • Aleksandrov Alexey
  • Simonson Thomas
  • Hinrichs Winfried
  Journal of Molecular Biology, Elsevier, 2010, 398 (1), pp.83-96. Secretory phospholipase A(2) is involved in inflammatory processes and was previously shown to be inhibited by lipophilic tetracyclines such as minocycline (minoTc) and doxycycline. Lipophilic tetracyclines might be a new lead compound for the design of specific inhibitors of secretory phospholipase A(2), which play a crucial role in inflammatory processes. Our X-ray crystal structure analysis at 1.65 A resolution of the minoTc complex of phospholipase A(2) (PLA(2)) of the Indian cobra (Naja naja naja) is the first example of nonantibiotic tetracycline interactions with a protein. MinoTc interferes with the conformation of the active-site Ca(2+)-binding loop, preventing Ca(2)(+) binding, and shields the active site from substrate entrance, resulting in inhibition of the enzyme. MinoTc binding to PLA(2) is dominated by hydrophobic interactions quite different from antibiotic recognition of tetracyclines by proteins or the ribosome. The affinity of minoTc for PLA(2) was determined by surface plasmon resonance, resulting in a dissociation constant K(d)=1.8 x 10(-)(4) M. (10.1016/j.jmb.2010.02.049)
  DOI : 10.1016/j.jmb.2010.02.049
• UV imaging of biochips based on resonant grating
  
  • Bougot-Robin Kristelle
  • Reverchon Jean-Luc
  • Benisty Henri
  • Fromant Michel
  • Plateau Pierre
  , 2010, 7673. In the frame of biological threat, security systems require label free biochips for rapid detection. Biosensors enable to detect biological interactions, between probes localized at the surface of a chip, and targets present in the sample solution. Here, we present an optical transduction, enabling 2D imaging, and consequently parallel detection of several reactions. It is based on the absorption of biological molecules in the UV domain. Thus, it is based on an intrinsic property of biological molecules and does not require any labelling of the biological molecules. DNA and proteins absorb UV light at 260 and 280 nm respectively. Sensitivity is a major requirement of biosensing devices. Configurations leading to enhancement of the interaction between light and biological molecules are of interest. For a better sensitivity, resonant grating structures are then studied. They enable to confine the electric field close to the biological layer. Imaging of resonant grating is not largely studied, even for visible wavelengths, but it results in good sensitivity. The protein used in this study is the methionyl-tRNA synthetase. Its absorption is representative of protein absorption, and it can then serve as a model for immunological detection. The best experimental contrast due to a monolayer of proteins is 40%. With data processing currently employed for biochip imaging: average on several acquisitions and on all the pixels imaging the biological spots, the device is able to detect a surface density of proteins in the 10 pg/mm range. © (2010) COPYRIGHT SPIE--The International Society for Optical Engineering (10.1117/12.854239)
  DOI : 10.1117/12.854239
• Far infrared spectra of solid state aliphatic amino acids in different protonation states.
  
  • Trivella Aurélien
  • Gaillard Thomas
  • Stote Roland H
  • Hellwig Petra
  The Journal of Chemical Physics, American Institute of Physics, 2010, 132 (11), pp.115105. Far infrared spectra of zwitterionic, cationic, and anionic forms of aliphatic amino acids in solid state have been studied experimentally. Measurements were done on glycine, L-alanine, L-valine, L-leucine, and L-isoleucine powder samples and film samples obtained from dried solutions prepared at pH ranging from 1 to 13. Solid state density functional theory calculations were also performed, and detailed potential energy distributions were obtained from normal mode results. A good correspondence between experimental and simulated spectra was achieved and this allowed us to propose an almost complete band assignment for the far infrared spectra of zwitterionic forms. In the 700-50 cm(-1) range, three regions were identified, each corresponding to a characteristic set of normal modes. A first region between 700 and 450 cm(-1) mainly contained the carboxylate bending, rocking, and wagging modes as well as the ammonium torsional mode. The 450-250 cm(-1) region was representative of backbone and sidechain skeletal bending modes. At last, the low wavenumber zone, below 250 cm(-1), was characteristic of carboxylate and skeletal torsional modes and of lattice modes. Assignments are also proposed for glycine cationic and anionic forms, but could not be obtained for all aliphatic amino acids due to the lack of structural data. This work is intended to provide fundamental information for the understanding of peptides vibrational properties. (10.1063/1.3356027)
  DOI : 10.1063/1.3356027
• Ligand-bound structures provide atomic snapshots for the catalytic mechanism of D-amino acid deacylase.
  
  • Bhatt T.K.
  • Yogavel M.
  • Wydau Sandra
  • Berwal R.
  • Sharma A.
  Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2010, 285 (8), pp.5917-30. D-tyrosyl-tRNA(Tyr) deacylase (DTD) is an editing enzyme that removes D-amino acids from mischarged tRNAs. We describe an in-depth analysis of the malaria parasite Plasmodium falciparum DTD here. Our data provide structural insights into DTD complexes with adenosine and D-amino acids. Bound adenosine is proximal to the DTD catalysis site, and it represents the authentic terminal adenosine of charged tRNA. DTD-bound D-amino acids cluster at three different subsites within the overall active site pocket. These subsites, called transition, active, and exit subsites allow docking, re-orientation, chiral selection, catalysis, and exit of the free D-amino acid from DTD. Our studies reveal variable modes of D-amino acid recognition by DTDs, suggesting an inherent plasticity that can accommodate all D-amino acids. An in-depth analysis of native, ADP-bound, and D-amino acid-complexed DTD structures provide the first atomic snapshots of ligand recognition and subsequent catalysis by this enzyme family. We have mapped sites for the deacylation reaction and mark possible routes for entry and egress of all substrates and products. We have also performed structure-based inhibitor discovery and tested lead compounds against the malaria parasite P. falciparum using growth inhibition assays. Our studies provide a comprehensive structural basis for the catalytic mechanism of DTD enzymes and have implications for inhibition of this enzyme in P. falciparum as a route to inhibiting the parasite. (10.1074/jbc.M109.038562)
  DOI : 10.1074/jbc.M109.038562
• Eukaryotic and archaeal translation initiation factor 2: a heterotrimeric tRNA carrier.
  
  • Schmitt Emmanuelle
  • Naveau Marie
  • Mechulam Yves
  FEBS Letters, Wiley, 2010, 584 (2), pp.405-12. Eukaryotic/archaeal translation initiation factor 2 (e/aIF2) is a heterotrimeric GTPase that plays a key role in selection of the correct start codon on messenger RNA. This review integrates structural and functional data to discuss the involvement of the three subunits in initiator tRNA binding. A possible role of the peripheral subunits in modulating the guanine nucleotide cycle on the core subunit is also addressed. (10.1016/j.febslet.2009.11.002)
  DOI : 10.1016/j.febslet.2009.11.002
• Alchemical free energy simulations for biological complexes: powerful but temperamental....
  
  • Aleksandrov Alexey
  • Thompson Damien
  • Simonson Thomas
  Journal of Molecular Recognition, Wiley, 2010, 23 (2), pp.117-27. Free energy simulations compare multiple ligand:receptor complexes by "alchemically" transforming one into another, yielding binding free energy differences. Since their introduction in the 1980s, many technical and theoretical obstacles were surmounted, and the method ("MDFE," since molecular dynamics are often used) has matured into a powerful tool. We describe its current status, its effectiveness, and the challenges it faces. MDFE has provided chemical accuracy for many systems but remains expensive, with significant human overhead costs. The bottlenecks have shifted, partly due to increased computer power. To study diverse sets of ligands, force field availability and accuracy can be a major difficulty. Another difficulty is the frequent need to consider multiple states, related to sidechain protonation or buried waters, for example. Sophisticated, automated methods to sample these states are maturing, such as constant pH simulations. Meanwhile, combinations of MDFE and simpler approaches, like continuum dielectric models, can be very effective. As illustrations, we show how, with careful force field parameterization, MDFE accurately predicts binding specificities between complex tetracycline ligands and their targets. We describe substrate binding to the aspartyl-tRNA synthetase enzyme, where many distinct electrostatic states play a role, and a histidine and a Mg(2+) ion act as coupled switches that help enforce a strict preference for the aspartate substrate, relative to several analogs. Overall, MDFE has achieved a predictive status, where novel ligands can be studied and molecular recognition elucidated in depth. It should play an increasing role in the analysis of complex cellular processes and biomolecular engineering. (10.1002/jmr.980)
  DOI : 10.1002/jmr.980
• Wolbachia Age-Sex-Specific Density in Aedes albopictus: A Host Evolutionary Response to Cytoplasmic Incompatibility?
  
  • Tortosa Pablo
  • Charlat Sylvain
  • Labbe Pierrick
  • Dehecq Jean-Sébastien
  • Barré Hélène
  • Weill Mylène
  PLoS ONE, Public Library of Science, 2010, 5 (3), pp.e9700. Background: Wolbachia bacteria have invaded many arthropod species by inducing Cytoplasmic Incompatibility (CI). These symbionts represent fascinating objects of study for evolutionary biologists, but also powerful potential biocontrol agents. Here, we assess the density dynamics of Wolbachia infections in males and females of the mosquito Aedes albopitcus, an important vector of human pathogens, and interpret the results within an evolutionary framework.Methodology/Principal Findings: Wolbachia densities were measured in natural populations and in age controlled mosquitoes using quantitative PCR. We show that the density dynamics of the wAlbA Wolbachia strain infecting Aedes albopictus drastically differ between males and females, with a very rapid decay of infection in males only.Conclusions/Significance: Theory predicts that Wolbachia and its hosts should cooperate to improve the transmission of infection to offspring, because only infected eggs are protected from the effects of CI. However, incompatible matings effectively lower the fertility of infected males, so that selection acting on the host genome should tend to reduce the expression of CI in males, for example, by reducing infection density in males before sexual maturation. The rapid decay of one Wolbachia infection in Aedes albopictus males, but not in females, is consistent with this prediction. We suggest that the commonly observed reduction in CI intensity with male age reflects a similar evolutionary process. Our results also highlight the importance of monitoring infection density dynamics in both males and females to assess the efficiency of Wolbachia-based control strategies (10.1371/journal.pone.0009700)
  DOI : 10.1371/journal.pone.0009700
• Computational protein design: validation and possible relevance as a tool for homology searching and fold recognition.
  
  • Schmidt Am Busch Marcel
  • Sedano Audrey
  • Simonson Thomas
  PLoS ONE, Public Library of Science, 2010, 5 (5), pp.e10410. BACKGROUND: Protein fold recognition usually relies on a statistical model of each fold; each model is constructed from an ensemble of natural sequences belonging to that fold. A complementary strategy may be to employ sequence ensembles produced by computational protein design. Designed sequences can be more diverse than natural sequences, possibly avoiding some limitations of experimental databases. METHODOLOGY/PRINCIPAL FINDINGS: WE EXPLORE THIS STRATEGY FOR FOUR SCOP FAMILIES: Small Kunitz-type inhibitors (SKIs), Interleukin-8 chemokines, PDZ domains, and large Caspase catalytic subunits, represented by 43 structures. An automated procedure is used to redesign the 43 proteins. We use the experimental backbones as fixed templates in the folded state and a molecular mechanics model to compute the interaction energies between sidechain and backbone groups. Calculations are done with the Proteins@Home volunteer computing platform. A heuristic algorithm is used to scan the sequence and conformational space, yielding 200,000-300,000 sequences per backbone template. The results confirm and generalize our earlier study of SH2 and SH3 domains. The designed sequences ressemble moderately-distant, natural homologues of the initial templates; e.g., the SUPERFAMILY, profile Hidden-Markov Model library recognizes 85% of the low-energy sequences as native-like. Conversely, Position Specific Scoring Matrices derived from the sequences can be used to detect natural homologues within the SwissProt database: 60% of known PDZ domains are detected and around 90% of known SKIs and chemokines. Energy components and inter-residue correlations are analyzed and ways to improve the method are discussed. CONCLUSIONS/SIGNIFICANCE: For some families, designed sequences can be a useful complement to experimental ones for homologue searching. However, improved tools are needed to extract more information from the designed profiles before the method can be of general use. (10.1371/journal.pone.0010410)
  DOI : 10.1371/journal.pone.0010410
• Computational Design in Synthetic Biology
  
  • Suarez Maria
  • Rodrigo Guillermo
  • Carrera Javier
  • Jaramillo Alfonso
  , 2010, pp.49-63. One of the most ambitious goals in biological engineering is the ability to computationally design an organism using unsupervised algorithms. We discuss the development of new automatic methodologies to design biological parts and devices using computational design. Some of them rely on the appropriate characterisation of single genetic elements into SBML models and their posterior assembly to generate the final transcriptional network with targeted behaviour (such as an oscillatory dynamics). This modular construction approach allows implementing a successful modelling-construction-characterization cycle. Currently, it is not clear what role is played by cellular context, and to which extent it is possible to fruitfully use such a modular approach, but the perspectives of a model-based design of biological networks overwhelms the corresponding risk