Etudes des assemblages biomoléculaires par RMN

L’étude des assemblages biomoléculaires de grande taille a été initiée au cours de la thèse de R. Sounier (bourse ministère de la recherche) dont j’ai assuré la formation et la co-direction depuis octobre 2004 avec Dr. Jean-Pierre Simorre (IBS, Grenoble). Deux premiers articles issusde ce travail ont déjà été publiés (Sounier et al. 2007; Schanda et al. 2007) et deux autres, avec R. Sounier en premier auteur, sont actuellement en préparation. Ces travaux ont débouché sur l’étude RMN hors d’équilibre de NanoMachines hyperthermophiles de plusieurs centaines de kDa. Ce dernier projet a été confié au Dr. C Amero qui a rejoint l’équipe en juin 2008, pour être formé sous ma direction à la RMN des assemblages supramoléculaires.J’ai également encadré, plusieurs étudiants en Master de Biologie de l’UJF. Ils ont été impliqués dans la mise au point de protocoles de protonation spécifique des méthyles des isoleucines pour K. Treche (2005) et des alanines pour N. Usé (2007). Deux étudiants en Masters de Physique ont été impliqués dans les développements pour l’attribution des ponts disulfures pour A. Sollier (1999) et M Falges (2006) pour la mesure rapide de RDC 1H-1H. Plus récemment, j’ai également formé J. Retel, un étudiant hollandais effectuant son stage de Master Life Science & Technology (programme commun des universités de Leiden et de Delft, NL 2007). Son travail de stage consiste à généraliser les outils développés lors de la thèse de Remy Sounier. Cette implication dans la formation des étudiants de Master a été validée par quatre articles dans lesquels les étudiants de Master sont co-auteurs (Boisbouvier et al. 2000; Scanda et al. 2007; Ayala et al., in press; Sounier et al., en préparation) et vient compléter l’expérienced’enseignement en Licence et Agrégation que j’ai acquise pendant deux ans de monitorat

Etudes biophysiques de l'interaction entre la protéine humaine TRBP et un précurseur de microARN oncogène

Les microARNs sont une classe de petits ARNs non codants qui régulent l'expression des gènes via un mecanisme d'interference par ARN. Les microARNs humains sont produits par une série de réactions enzymatiques. En particulier, dans le cytoplasme le precurseur de miRNA (pre-miRNA) est reconnu et clivé par un complexe contenant l'enzyme RNAse III Dicer et plusieurs cofacteurs protéiques. La proteine TRBP (HIV TAR RNA binding protein) est l'un de ces cofacteurs et augmente la stabilité du complexe, influe sur la cinétique, la position du clivage et a role potentiel dans la reconnaissance du substrat et dans le transfet du produit vers le complexe RISC (RNA-induced silencing complex) effecteur de l'interference par ARN. TRBP est composé de 3 domaines de liaison aux ARN doubles brin (dsRBDs). La région d'interaction de TRBP avec les ARNs est composé des deux premiers dsRBDs liés par une région interdomaine non charactérizée. La présente étude rapporte la caractérisation biophysique in vitro de la région d'interaction avec les ARNs de TRBP dans l'état apo de TRBP ou dans l'état lié avec les deux precurseurs cytoplasmique successifs du microARN oncogène miR-155 comprenant la tige boucle pre-miR-155 et le duplex miR-155/miR-155* résultat du clivage de pre-miR-155 par Dicer. L'étude montre que la région d'intéraction de TRBP avec les ARNs est monomerique, est composée de deux dsRBDs independants en solution et que la région interdomaine de 60 résidus est flexible. Le premier dsRBD, non caractérisé précédement en solution est le siège d'un equilibre plié/déplié integral dans une grande gamme de conditions physico-chimiques. Les deux premiers dsRBDs de TRBP peuvent interagir avec un même precurseur de microARN et deux régions d'interaction de TRBP avec les ARNs peuvent interagir avec un même precuseur. La région d'interaction de TRBP avec les ARNs interagit avec pre-miR-155 et le duplex miR-155/miR-155* avec des affinités très similaires. Dans le complexe avec une région d'interaction de TRBP avec les ARN liée à pre-miR-155 ou au duplexe miR-155/miR-155*, aucune indice de contact entre les deux dsRBDs n'a été detecté et la protéine interagit avec les deux precurseurs par la même surface d'interaction. Les informations récoltées suggèrent que TRBP peut jouer un rôle avant et après le clivage des pre-miARN par Dicer, notamment dans le complexe de chargement de RISC.MicroRNAs (miRNA) are a class of small non-coding RNAs that regulate gene expression through RNA interference (RNAi). Human miRNAs are generated via a series of enzymatic processing steps. In particular, in the cytoplasm, the precursor miRNA (pre-miRNA) is recognized and cleaved by a complex containing the RNase III enzyme Dicer and several non-catalytic accessory proteins. HIV TAR element-binding protein (TRBP) is a constituent of the Dicer complex, which augments complex stability, has effect on the cleavage kinetics and on the cleavage site and potentially functions in substrate recognition and product transfer to the RNA-induced silencing complex (RISC). TRBP is composed of three double stranded RNA binding domains (dsRBDs). The RNA binding region of TRBP is composed of the first two dsRBDs and an uncharacterized interdomain region. The present study reports the in vitro biophysical characterization of the RNA binding region of TRBP in the apo state and in the RNA bound state with the two successive cytoplasmic precursors of the oncogenic human microRNA miR-155, the hairpin pre-miR-155 and the related Dicer product miR-155/miR-155* duplex. The study shows that the RNA binding region of TRBP is monomeric and comprises two independent double-stranded RNA-binding domains connected by a 60 residues flexible linker. The first dsRBD, uncharacterized previously in solution, undergoes a full folding/unfolding equilibrium in a wide range of physico-chemical conditions. The two first dsRBDs of TRBP can interact with one microRNA precursor and two RNA binding regions can interact with one precursor molecule. The RNA-binding region of TRBP interacts with both pre-miR-155 and miR-155/miR-155* duplex with similar affinities. In the complex with one RNA binding region of TRBP bound to either pre-miR-155 or miR-155/miR-155* duplex, no evidence of contact between the two dsRBDs were observed and the protein interacts with both precursors via the same protein binding surface. The data presented here suggest that the RNA binding region of TRBP can play a role before and after processing of pre-miRNAs by Dicer, including in the RISC loading complex.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Sensitive proton-detected solid-state NMR spectroscopy of large proteins with selective CH3 labelling: application to the 50S ribosome subunit

International audienceSolid-state NMR spectroscopy allows the characterization of structure, interactions and dynamics of insoluble and/or very large proteins. Sensitivity and resolution are often major challenges for obtaining atomic-resolution information, in particular for very large protein complexes. Here we show that the use of deuterated, specifically CH3-labelled proteins result in significant sensitivity gains compared to previously employed CHD2 labelling, while line widths only marginally increase. We apply this labelling strategy to a 468 kDa-large dodecameric aminopeptidase, TET2, and the 1.6 MDa-large 50S ribosome subunit of Thermus thermophilus

NMR structure of the A730 loop of the Neurospora VS ribozyme: insights into the formation of the active site

The Neurospora VS ribozyme is a small nucleolytic ribozyme with unique primary, secondary and global tertiary structures, which displays mechanistic similarities to the hairpin ribozyme. Here, we determined the high-resolution NMR structure of a stem–loop VI fragment containing the A730 internal loop, which forms part of the active site. In the presence of magnesium ions, the A730 loop adopts a structure that is consistent with existing biochemical data and most likely reflects its conformation in the VS ribozyme prior to docking with the cleavage site internal loop. Interestingly, the A730 loop adopts an S-turn motif that is also present in loop B within the hairpin ribozyme active site. The S-turn appears necessary to expose the Watson–Crick edge of a catalytically important residue (A756) so that it can fulfill its role in catalysis. The A730 loop and the cleavage site loop of the VS ribozyme display structural similarities to internal loops found in the active site of the hairpin ribozyme. These similarities provided a rationale to build a model of the VS ribozyme active site based on the crystal structure of the hairpin ribozyme

Advanced isotopic labeling for the NMR investigation of challenging proteins and nucleic acids

International audienc

CH3-specific NMR assignment of alanine, isoleucine, leucine and valine methyl groups in high molecular weight proteins using a single sample

International audienceA new strategy for the NMR assignment of aliphatic side-chains in large perdeuterated proteins is proposed. It involves an alternative isotopic labeling protocol, the use of an out-and-back C-13-C-13 TOCSY experiment ((H)C-TOCSY-C-TOCSY-(C)H) and an optimized non-uniform sampling protocol. It has long been known that the non-linearity of an aliphatic spin-system (for example Ile, Val, or Leu) substantially compromises the efficiency of the TOCSY transfers. To permit the use of this efficient pulse scheme, a series of optimized precursors were designed to yield linear C-13 perdeuterated side-chains with a single protonated CH3 group in these three residues. These precursors were added to the culture medium for incorporation into expressed proteins. For Val and Leu residues, the topologically different spin-systems introduced for the pro-R and pro-S methyl groups enable stereospecific assignment. All CH3 can be simultaneously assigned on a single sample using a TOCSY experiment. It only requires the tuning of a mixing delay and is thus more versatile than the relayed COSY experiment. Enhanced resolution and sensi-tivity can be achieved by non-uniform sampling combined with the removal of the large J(CC) coupling by deconvolution prior to the processing by iterative soft thresholding. This strategy has been used on malate synthase G where a large percentage of the CH3 groups could be correlated directly up to the backbone Ca. It is anticipated that this robust combined strategy can be routinely applied to large proteins

A simple biosynthetic method for stereospecific resonance assignment of prochiral methyl groups in proteins

International audienceA new method for stereospecific assignment of prochiral methyl groups in proteins is presented in which protein samples are produced using U-[13C]glucose and subsaturating amounts of 2-[13C]methyl-acetolactate. The resulting non-uniform labeling pattern allows proR and proS methyl groups to be easily distinguished by their different phases in a constant-time two-dimensional 1H-13C correlation spectra. Protein samples are conveniently prepared using the same media composition as the main uniformly-labeled sample and contain higher levels of isotope-enrichment than fractional labeling approaches. This new strategy thus represents an economically-attractive, robust alternative for obtaining isotopically-encoded stereospecific NMR assignments of prochiral methyl groups

Induced folding in RNA recognition by Arabidopsis thaliana DCL1

DCL1 is the ribonuclease that carries out miRNA biogenesis in plants. The enzyme has two tandem double stranded RNA binding domains (dsRBDs) in its C-terminus. Here we show that the first of these domains binds precursor RNA fragments when isolated and cooperates with the second domain in the recognition of substrate RNA. Remarkably, despite showing RNA binding activity, this domain is intrinsically disordered. We found that it acquires a folded conformation when bound to its substrate, being the first report of a complete dsRBD folding upon binding. The free unfolded form shows tendency to adopt folded conformations, and goes through an unfolded bound state prior to the folding event. The significance of these results is discussed by comparison with the behavior of other dsRBDs.This article has been accepted for publication in Nucleic Acids Research Published by Oxford University Press.Fil: Suárez, Irina Paula. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina.Fil: Suárez, Irina Paula. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Área Biofísica; Argentina.Fil: Burdisso, Paula. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina.Fil: Burdisso, Paula. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Área Biofísica; Argentina.Fil: Benoit, Matthieu P. M. H. Commissariat à l’énergie atomique et aux énergies alternatives (CEA). Institut de Biologie Structurale Jean-Pierre Ebel (IBS); France.Fil: Benoit, Matthieu P. M. H. Centre National de la Recherche Scientifique (CNRS). Institut de Biologie Structurale Jean-Pierre Ebel (IBS); France.Fil: Benoit, Matthieu P. M. H. Université Joseph Fourier. Institut de Biologie Structurale Jean-Pierre Ebel (IBS); France.Fil: Boisbouvier, Jérôme. Commissariat à l’énergie atomique et aux énergies alternatives (CEA). Institut de Biologie Structurale Jean-Pierre Ebel (IBS); France.Fil: Boisbouvier, Jérôme. Centre National de la Recherche Scientifique (CNRS). Institut de Biologie Structurale Jean-Pierre Ebel (IBS); France.Fil: Boisbouvier, Jérôme. Université Joseph Fourier. Institut de Biologie Structurale Jean-Pierre Ebel (IBS); France.Fil: Rasia, Rodolfo M. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina.Fil: Rasia, Rodolfo M. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Área Biofísica; Argentina.This article has been accepted for publication in Nucleic Acids Research Published by Oxford University Press

Pi7, an orphan peptide from the scorpion Pandinus imperator: a 1H-NMR analysis using a nano-NMR Probe.

International audienceThe three-dimensional solution structure of a novel peptide, Pi7, purified from the venom of the scorpion Pandinus imperator, and for which no specific receptor has been found yet, was determined by two-dimensional homonuclear proton NMR methods from a nanomole amount of compound using a nano-nmr probe. Pandinus imperator peptide 7 does not block voltage-dependent K(+)-channels and does not displace labeled noxiustoxin from rat brain synaptosomal membranes. The toxin has 38 amino acid residues and, similarly to Pi1, is stabilized by four disulfide bridges (Cys6-Cys27, Cys12-Cys32, Cys16-Cys34, and Cys22-Cys37). In addition, the lysine at position 26 crucial for potassium-channel blocking is replaced in Pi7 by an arginine. Tyrosine 34, equivalent to Tyr36 of ChTX is present, but the N-terminal positions 1 and 2 are occupied by two acidic residues Asp and Glu, respectively. The dihedral angles and distance restraints obtained from measured NMR parameters were used in structural calculations in order to determine the conformation of the peptide. The disulfide-bridge topology was established using distance restraints allowing ambiguous partners between S atoms combined with NMR-derived structural information. The structure is organized around a short alpha-helix spanning residues Thr9 to Thr20/Gly21 and a beta-sheet. These two elements of secondary structure are stabilized by two disulfide bridges, Cys12-Cys32 and Cys16-Cys34. The antiparallel beta-sheet is composed of two strands extending from Asn22 to Cys34 with a tight turn at Ile28-Asn29 in contact with the N-terminal fragment Ile4 to Cys6

Specific labeling and assignment strategies of valine methyl groups for NMR studies of high molecular weight proteins

International audienceThe specific protonation of valine and leucine methyl groups in proteins is typically achieved by overexpressing proteins in M9/D2O medium supplemented with either labeled α-ketoisovalerate for the labeling of the four prochiral methyl groups or with 2-acetolactate for the stereospecific labeling of the valine and leucine side chains. However, when these labeling schemes are applied to large protein assemblies, significant overlap between the correlations of the valine and leucine methyl groups occurs, hampering the analysis of 2D methyl-TROSY spectra. Analysis of the leucine and valine biosynthesis pathways revealed that the incorporation of labeled precursors in the leucine pathway can be inhibited by the addition of exogenous l-leucine-d10. We exploited this property to label stereospecifically the pro-R and pro-S methyl groups of valine with minimal scrambling to the leucine residues. This new labeling protocol was applied to the 468 kDa homododecameric peptidase TET2 to decrease the complexity of its NMR spectra. All of the pro-S valine methyl resonances of TET2 were assigned by combining mutagenesis with this innovative labeling approach. The assignments were transferred to the pro-R groups using an optimally labeled sample and a set of triple resonance experiments. This improved labeling scheme enables us to overcome the main limitation of overcrowding in the NMR spectra of prochiral methyl groups, which is a prerequisite for the site-specific measurement of the structural and dynamic parameters or for the study of interactions in very large protein assemblies