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National audience; Alpha-1 antitrypsin deficiency is a frequent genetic disorder associated with pulmonary emphysema in smokers and with liver cirrhosis. Aside from lung or liver transplantation, only replacement therapy can currently slow the progression of emphysema. Progress in the pathogenesis of this disorder (protein misfolding, RER aggregation) is opening the way to new strategies such as proteostasis control. Alpha-1 antitrypsin deficiency remains poorly known and underdiagnosed.

National audience

The primary function of peptide N-glycanase (PNGase) is thought to be the deglycosylation of endoplasmic reticulum associated degradation (ERAD) substrates. However, inhibition of PNGase appears to have little effect upon the destruction rate of many ERAD substrates, and recent data demonstrate deglycosylation-independent functions for PNGase. Whatever the roles of PNGase turn out to be, the identification of a patient presenting with PNGase deficiency will advance our understanding of the importance of this multifunctional protein in human physiology.

RVV Plant virology meeting (January 27-31, 2019, Aussois, France) allows researchers, engineers, technicians, students and post-docs to exchange around oral and poster presentations. These convivial meetings are 30 years old and have a nice future.

International audience; Several progressive neurodegenerative disorders, e.g. Alzheimer, Parkinson and Huntington diseases, cerebro-spinal ataxia and amyotrophic lateral sclerosis, are the consequence of protein misfolding and aggregation. Recent data indicates that some of these diseases are not cell autonomous as previously thought. We and others have shown that protein assemblies involved in the aforementioned diseases propagate from cell to cell in a manner akin prion high molecular weight assemblies propagation in Creutzfeldt-Jacob disease. The mechanism of propagation and amplification of protein assemblies involved in neurodegenerative diseases and its physiopathological consequences are discussed hereafter.

The ABC transporter ABCB4 is a phosphatidylcholine translocator expressed at the bile canalicular membrane of hepatocytes. Variations of the ABCB4 gene have been recognized as causing progressive familial intrahepatic cholestasis type 3 (PFIC3) in children, a rare lethal disorder which progresses to cirrhosis and liver failure before adulthood. We studied the effect of the I541F mutation described in a PFIC3 patient. In contrast to wild-type ABCB4 which was localized at the bile canalicular membrane in HepG2 cells and at the apical surface in MDCK cells after stable transfection, the I541F mutant did not fold properly and accumulated in the endoplasmic reticulum (ER). After shifting cells to 27°C, the mutant was expressed at the apical cell surface in a mature and active form. Modulation of the cellular chaperones calnexin and Hsc/Hsp70 did not restore intracellular trafficking of the mutant. Cyclosporin A improved maturation and plasma membrane expression of ABCB4-I541F, thus opening perspectives to develop novel therapies for the treatment of PFIC3. The second part of the study was aimed at identifying the role of the N-terminal cytoplasmic domain of ABCB4, which does not show homology with other ABC transporters. Progressive deletions of the N-terminus identified a positively charged sequence of 11 amino-acids, which is required for exit of the ER. Single point mutations (T34M and R47G) identified in patients did not affect processing and trafficking, but strongly decreased the function of ABCB4. These results show that the N-terminal domain is required for both trafficking and function of ABCB4, ABCB4 est un transporteur ABC spécialisé dans la sécrétion de phosphatidylcholine au niveau de la membrane canaliculaire des hépatocytes. Des variations du gène ABCB4 sont responsables de la cholestase intrahépatique familiale progressive de type 3 (PFIC3), une maladie rare, létale, qui progresse en cirrhose et insuffisance hépatique avant l'âge adulte. Nous avons étudié l'effet de la mutation I541F décrite chez un patient. Contrairement à la forme sauvage d'ABCB4 localisée à la membrane des canalicules biliaires dans les cellules HepG2 et à la surface apicale dans les cellules MDCK transfectées, le mutant I541F n'est pas replié correctement et s'accumule dans le réticulum endoplasmique (RE). Après transfert à 27°C, le mutant est exprimé à la surface apicale sous forme mature et active. La modulation des chaperonnes cellulaires calnexine et Hsc/Hsp70 ne restaure pas le trafic intracellulaire du mutant. La cyclosporine A augmente la maturation et l'expression à la membrane plasmique d'ABCB4-I541F, ce qui ouvre des perspectives de développer de nouvelles thérapies pour le traitement de la PFIC3. La seconde partie du travail a eu pour objectif de déterminer le rôle du domaine cytoplasmique N-terminal d'ABCB4, qui n'a pas d'homologie avec d'autres transporteurs ABC. Des délétions progressives de ce domaine ont permis d'identifier une séquence de 11 acides aminés nécessaire à la sortie du RE. Des mutations ponctuelles (T34M et R47G) identifiées chez des patients n'affectent pas la maturation ni le trafic, mais diminuent fortement l'activité d'ABCB4. Ces résultats montrent que le domaine N-terminal est nécessaire à la fois pour le trafic et l'activité d'ABCB4

Basic research on prions and on protein and peptide aggregation generated a new vision of the pathologic mechanisms of many disorders regrouped under the term "proteinopathies". The latter include several neurodegenerative disorders (Alzheimer, Parkinson disease...) which could benefit for their diagnosis and therapeutics of this type of research. Importantly, the presence of proteins behaving like prions in yeast also contributed to the advance of knowledge in this area by showing that the transmission of a conformational information could be considered as a new epigenetic mechanism. In addition yeast models allow to study the molecular mechanism of protein aggregation, the role of accessory factors, like chaperones, and the screening of therapeutic agents.

Amyloid peptides and proteins are associated with several diseases named amyloidoses. These proteins, in conditions that are still unclear, fold into cross-β-sheet structures and form fibrils. In order to gain insight into the folding process, we have designed models of amyloid fibrils by the synthesis of polypeptidic edifices based on the sequence of the β amyloid peptide. They are made of two or four mutated, linear or cyclic, β-amyloid fragments covalently attached to a cyclic decapeptide scaffold. These polypeptidic edifices fold into cross-β-sheet structures and polymerize into protofilaments with diameters of 5-6 nm. Using molecular modelling, we have demonstrated that the folding in β strand-loop-β strand structure and a central hydrophobic core are required for the formation of the parallel cross β sheet structures. These edifices are promising models that will allow a better understanding of the amyloid fibril formation.Among the therapeutic approaches in development to fight amyloidoses, the inhibition of the fibril formation has been widely investigated. In this work we have developed inhibitors of fibrillogenesis by the attachment of hydrophobic compounds on the cyclic decapeptide. The aim of this strategy is to create an important area of interaction with the amyloid β peptide and thus disturb its self-assembly process. We have shown by performing Aβ40 polymerization assays that these compounds are very efficient inhibitors which contrast with monomeric analogues. These results support the interest of this strategy to interfere with the amyloid fibril formation.; Les peptides et protéines amyloïdes sont impliqués dans de nombreuses pathologies regroupées sous le terme d'amyloses. Ces protéines, dans des conditions encore mal connues, se replient en feuillets β croisés et s'assemblent en fibres. Afin de comprendre les principes physico-chimiques impliqués dans ce processus, nous avons conçu des modèles de fibres amyloïdes par la synthèse d'édifices peptidiques basés sur la séquence du peptide β amyloïde. Ils se composent de deux ou quatre fragments amyloïdes mutés, linéaires ou cyclisés, que nous avons liés à un châssis décapeptide cyclique. Ces édifices se replient en feuillets β croisés et s'assemblent en protofilaments de 5 à 6 nm de diamètre. A l'aide de la modélisation moléculaire, nous avons montré que le repliement en boucle de type brin β-boucle-brin β et la création d'un cœur hydrophobe sont nécessaires pour la formation des feuillets β croisés parallèles. Ces édifices sont des modèles très prometteurs pour la compréhension du mécanisme de formation des fibres amyloïdes.Parmi les stratégies thérapeutiques développées récemment pour lutter contre les amyloses, l'inhibition de la formation des dépôts amyloïdes a été largement étudiée. Au cours de nos travaux, nous avons développé des inhibiteurs de la fibrillogénèse par la présentation de plusieurs exemplaires de molécules hydrophobes sur un cyclodécapeptide. Cette stratégie a pour but de créer une zone d'interaction avec le peptide β amyloïde suffisamment importante pour perturber son auto-association. Nous avons montré, par la réalisation d'expériences de polymérisation du peptide Aβ40, que ces composés sont des inhibiteurs très efficaces par comparaison avec les dérivés monomériques. Ces résultats confirment l'intérêt de cette stratégie pour interférer avec le phénomène de formation des fibres amyloïdes.

Protein folding is the last stage of genetic expression. The mechanism by which proteins acquire their 3D structure remains poorly understood. During my project, I showed that the addition of one residue in one loop of the structure of toxin a from Naja nigricollis slows its oxidative folding process down in vitro. This decrease in the folding rate is due to a switch of productive pathway. NMR analysis of folding intermediates enabled me to hypothesize a structural explantation for this kinetic modification. Additionally, in order to test the influence of vectorial folding on the folding of a small disulfide-rich protein in vitro, I developed a method using antibodies raised against various parts of the reduced protein. My results showed that one of these antibodies is able to inhibit the oxidative folding of toxin a. This inhibition is reversible. Most interestingly, the use of this antibody modifies the folding pathway.; Le repliement des protéines, dernière étape du processus d'expression de l'information génétique, demeure imparfaitement expliqué. Pendant ma thèse, j'ai étudié le repliement oxydant d'une petite protéine riche en ponts disulfure, la toxine a de Naja nigricollis. J'ai pu montrer que l'addition d'un acide aminé dans une boucle de la structure entraîne un ralentissement global du repliement in vitro causé par une permutation des intermédiaires productifs. L'étude en RMN des intermédiaires de repliement a permis de proposer une explication structurale à cette modification de comportement cinétique. Par ailleurs, pour tester l'importance de l'aspect vectoriel du repliement in vivo, j'ai développé une méthode ayant pour but de vectoriser le repliement in vitro. J'ai pu montrer qu'il est possible grâce à des anticorps dirigés contre la toxine a réduite d'inhiber son repliement oxydant, de lever cette inhibition et finalement de modifier sa voie de repliement.

Increasing our understanding of the cellular and molecular mechanisms of acute and chronic kidney diseases will lead to the development of new biomarkers of early kidney injury and to the discovery of new therapeutic strategies to prevent the initiation of renal failure or to promote the renal regeneration after injury. The implication of the endoplasmic reticulum stress in kidney diseases is not well recognized, but increasing experimental evidences suggest its implication in a wide array of kidney insults. Beside its role in the regulation of cell death, the UPR response induced by the endoplasmic reticulum stress alters many cellular functions and constitutes an important mediator of inflammation and/or epithelial to mesenchymal transition. The purpose of this review is to summarize the existing data concerning the role of the endoplasmic reticulum stress during kidney injury and to clarify its precise role in chronic kidney disease.

Protein folding is one of the central questions of Biology. How does polypeptidic chain fold to its three-dimensional, biologically active, structure? Experiments done in the 60?s have shown that the folded form is the most stable one on a thermodynamic point of view. This form being defined by the primary structure of the protein, the folding reaction corresponds to the last step of the use of the information encoded in DNA. Proteins can sometimes misfold and form amyloid fibrils through intermolecular interactions. These structured aggregates are involved in several diseases such as Alzheimer?s disease, Parkinson diseases...These phenomenon's are studied here in the case of alpha-lactalbumin, a milk protein which possesses a calcium binding site. At first, the folding is monitored in presence of various metal ions that bind to the calcium site. These experiments are coupled with thermal unfolding experiments. They permit to precise the effect of metal ion binding on the different states of the protein and on the folding kinetics.The reaction is also monitored in the absence of metal ions with several biophysical methods. Then, the folding is much slower and intricate. A reaction scheme is drawn from the results. This scheme indicates that a state precursor of amyloid fibril is transiently populated during the reaction. Finally, the effect of intermolecular interactions on the formation of amyloid fibrils is characterized for different salt concentrations., Le repliement des protéines est un des problèmes centraux de la biologie. Il s'agit de comprendre comment la chaîne polypeptidique d'une protéine se replie pour acquérir sa structure tridimensionnelle biologiquement active. Il a été démontré dans les années 60 que la forme repliée de la protéine est le plus stable d'un point de vue thermodynamique et qu'il est défini par la structure primaire. La réaction de repliement correspond ainsi à la dernière étape de l'utilisation de l'information contenue dans l'ADN. Cependant, Il est possible que les protéines se replient mal et interagissent entre elles pour former des fibres amyloïdes. Ce sont des agrégats structurés impliqués dans plusieurs maladies comme la maladie d'Alzheimer, de Parkinson... Ces phénomènes sont étudiés ici dans le cas de l'alpha-lactalbumine, une protéine du lait qui possède un site de liaison pour le calcium. Le repliement est tout d'abord étudié en présence de métaux se liant au site du calcium. Ces expériences sont couplées à des expériences de dénaturation thermiques pour caractériser le rôle de la fixation des métaux sur les différents états de la protéine et son influence sur la cinétique de repliement.La réaction est ensuite caractérisée en absence d'ion métallique. Elle est alors beaucoup plus lente et complexe. Différentes techniques spectroscopiques sont utilisées. Les résultats obtenus permettent de proposer un schéma réactionnel selon lequel un état précurseur de fibres amyloïdes est transitoirement peuplé. Enfin, pour compléter cette étude, les effets des interactions entre protéines sur la formation de fibres amyloïdes ont été étudiés pour différentes concentrations en sel.

Prion-based diseases are fatal neurodegenerative disorders for which no efficient treatment is currently available. We focussed our work on the identification of the intracellular biochemical targets of two drugs 6AP and GA, isolated in the laboratory as antiprion drugs using a yeast-based assay to uncover biochemical pathways controlling prion formation. Using both genetic and biochemical approaches, we show an RNA-dependent interaction of 6AP and GA with ribosomes. 6AP and GA specifically inhibit the protein folding activity of the large ribosomal RNA of the large ribosome subunit. We thus propose that the ribosomal RNA protein folding activity is required for prion maintenance. These drugs are also efficient against other protein misfolding diseases: Huntington disease or cystic fibrosis. 6AP and GA could have much wider applications than in prion diseases.; Les maladies à prions sont des maladies neurodégénératives touchant l’homme ainsi que l’animal et dont l’issue est toujours fatale. Notre objectif était d’utiliser la 6AP et le GA, deux drogues antiprion isolées au laboratoire comme des hameçons moléculaires pour identifier leurs cibles cellulaires afin de mieux comprendre leur mode d’action ainsi que les phénomènes de prionisation. Deux criblages, l’un génétique et l’autre biochimique ont révélé que les chaperons de protéines et les ribosomes sont impliqués. Les drogues antiprion testées ciblent spécifiquement la fonction de repliement des protéines portée par le grand ARNr 23S/25S/28S. Ceci suggère que l’activité de chaperon de protéines du grand ARNr est nécessaire pour le maintien et la propagation des prions. Ces molécules semblent aussi être actives contre d’autres maladies liées à des problèmes de repliement et d’agrégation des protéines. Nos molécules ont donc un avenir potentiel dans le traitement de ces maladies.

The endoplasmic reticulum (ER) is the first compartment in the secretory pathway. In the ER, proteins fold into their native configuration and are modified by post-translational modifications. Perturbations that alter ER homeostasis therefore disrupt folding and lead to the accumulation of unfolded proteins. These perturbations include modifications of Ca2+ homeostasis, increased demand for protein folding due to elevated synthesis of proteins in specialized cells or expression of a mutant misfolded protein. To limit accumulation of unfolded proteins, the cells have developed a specialized pathway : the unfolded protein response (UPR). UPR involves the activation of three transmembrane proteins of the ER : the PKR-like ER protein kinase (PERK), the activating transcription factor 6 (ATF6) and the inositol requiring enzyme 1 (IRE-1). The activation of all three components of the UPR depends on the dissociation of the luminal chaperone BiP/GRP78 from the luminal part of these proteins. Once activated, these pathways down-regulate protein synthesis through the phosphorylation of eiF2 (eucaryotic translation initiation factor 2) and up-regulate the transcription of genes which encode ER chaperones, protein folding enzymes and components of the ER-associated degradation system (ERAD). Growing evidences indicate that UPR signaling plays critical roles in nutrient sensing, differentiation of secretory cells such as pancreatic b cell and antibody producing plasma cells, glucose homeostasis and in the development of pathologies linked to accumulation of aggregated proteins.

Under various stresses, mutation-sensitised proteins may spontaneously convert into inactive, aggregation-prone structures, which may be cytotoxic and infectious. In the cell, this new kind of "molecular criminality" is actively fought against by a network of molecular chaperones that can specifically identify, isolate and unfold damaged (delinquent) proteins and favour their subsequent native refolding. Irreversibly damaged molecules unable to natively refold are preferentially "executed" and recycled by proteases. Failing that, they are "imprisoned" within compact amyloids, or "evicted" from the cell. Thus, striking parallels, although of questionable ethical value, exist between protein and human criminality, and between the cellular and social responses to these different types of criminality. Fundamental differences also exist. Whereas programmed death (apoptosis) is the preferred solution chosen by aged and aggregation-stressed cells, collective suicide is seldom an option chosen by lawless human societies. More significantly, there is no clear cellular equivalent for the role of the family and the education system, which are so essential to the proper shaping of functional individuals in the society, and give rise to humanism, that favours crime prevention, reeducation and reinsertion programs over capital punishment. To the cardiologist and transplantation surgeon, the interest of molecular chaperones, in particular of Hsp70, Hsp90 and Hsp27, lays in their ability to inhibit the signalling pathway of programmed cell death. Their induction before and during ischemia, by various treatments and drugs could significantly reduce damages from the post ischemic reperfusion of organs.

The human thyroperoxidase (TPO) is the main enzyme involved in thyroid hormone synthesis. This type I membrane-bound glycoprotein expressed at the apical surface of thyrocytes catalyzes both the iodination of thyroglobulin and the coupling of some of the iodotyrosyl residues required for the formation of T3 and T4 thyroid hormones.During its biosynthesis, the hTPO undergoes post-transcriptional mRNA modification by alternative splicing. Three isoforms have been already described: the hTPO1 (full lenght cDNA), the hTPO2 and the hTPO3 in which exons 10 and 16 are respectively spliced out. During my PhD, we identified and quantified by PCR, five novel spliced isoforms: the hTPO4 (- exon 14), the hTPO5 (- exon 8), the hTPO6 (- exons 10,12,13,14 and 16), the hTPO2/4 (- exons 10 and 14) and the hTPO2/3 (- exnos 10 and 16). These new spliced variants code for proteins with different stability, subcellular localization and enzymatic properties. Moreover we also showed that these splicing events increased in benign and malignant thyroid tissues and could be involved in the loss-of-function of thyroid hormones production observed in tumoral thyroid pathologies.The hTPO undergoes co- and post-traductional modifications. In the endoplasmic reticulum the protein interact with a set of molecular « chaperone » involved in the properly folding and the quality control machinery of proteins, like calnexin (CNX) and calreticulin. We showed that the surexpression of CNX and its thiol oxido-reductase partner Erp57 did not increased the properly folding rate of the hTPO1. Contrary to CNX, we show that BiP, an other folding protein helper, impaired the maturation process and target hTPO for degradation. In the case of hTPO, BiP seems to be a sensor of the protein degradation pathway. In a final set of experiments, we identified an N-terminal endoproteolytic cleavage of both hTPO purified from human thyroid gland and extracted from CHO cells. The enzyme implicated in the cleavage belong to the subtilisin-like proteases family, implicated in the maturation process of various receptors and surface proteins. As for the human myeloperoxidase, the prosequence of the hTPO acts as an internal molecular chaperone, helping the proper folding process of the protein.All together, these results enlarged your understanding of mechanisms involved in the maturation of the hTPO and proposed an additional explanation of the heterogeneity of the hTPO expressed in the human thyroid gland., La thyroperoxydase humaine (hTPO) est l'enzyme clé de la biosynthèse des hormones thyroïdiennes, impliquées dans de nombreux processus biologiques. Cette hémo- glycoprotéine membranaire de type I est exprimée à la surface apicale des thyrocytes où elle exerce ses fonctions d'iodation de certains résidus de tyrosine de la thyroglobuline et de couplage de ces iodotyrosines pour former les hormones thyroïdiennes T3 et T4. Lors de sa biosynthèse, la hTPO subit des modifications post-transcriptionnelles par épissage alternatif du précurseur de l'ARNm. Trois isoformes de l'enzyme étaient connues : la TPO1 (ADNc complet), la TPO2 et la TPO3 engendrées par épissage alternatif des exons 10 et 16 du précurseur de l'ARNm de la TPO. Dans cette thèse, nous avons identifié et quantifié par PCR, cinq nouvelles isoformes toutes induites par des épissages alternatifs : la TPO4 (sans exon 14), la TPO5 (sans exon 8), la TPO6 (sans exons 10, 12, 13, 14 et 16), la TPO2/4 (sans exons 10 et 14), et la TPO2/3 (sans exons 10 et 16). Ces isoformes sont plus ou moins stables, actives ou non et transportées correctement ou non jusqu'à la membrane plasmique. Nous avons également démontré, comme pour d'autres cas de pathologie cancéreuse, l'augmentation des phénomènes d'épissage alternatif de la hTPO en association avec une diminution globale du taux d'expression transcriptionnel de la protéine dans les différents types de cancers thyroïdiens. La hTPO subit également des modifications co- et post-traductionnelles. Elle interagit en particulier avec les « protéines chaperons » du réticulum endoplasmique (RE), qui aident les protéines nouvellement synthétisées à se replier correctement et font partie du “contrôle de qualité” du RE. On sait que la hTPO est largement retenue au niveau du réticulum endoplasmique et subissait un processus de dégradation faisant intervenir d'une part le protéasome et d'autre part des protéases du RE. Le repliement correct de la hTPO nécessite des interactions avec la calnexine (CNX) et la calreticuline. Dans cette thèse, nous montrons que la co-surexpression de la CNX et de ERp57, impliquée dans la formation des ponts disulfures des protéines interagissant avec la CNX, n'augmente pas la proportion des formes correctement repliées, ce qui suggère l'implication d'autres protéines chaperons et/ou de catalyseurs de repliement dans le processus de maturation de la hTPO. Nous montrons qu'à l'inverse de la CNX, l'interaction avec une autre protéine chaperon appelée BiP, diminue le repliement de la hTPO et entraîne la protéine vers la dégradation, suggérant ainsi que BiP pourrait être un des senseurs de la dégradation de la hTPO. Nous avons aussi montré que la thyroperoxydase purifiée à partir de thyroïde humaine ou exprimée dans les CHO subit un clivage endoprotéolytique dans sa partie N-terminale. L'enzyme impliquée dans ce clivage appartient vraisemblablement à la famille des protéines convertases, endoprotéases impliquées dans la maturation de nombreux précurseurs de pro-récepteurs et glycoprotéines de surface. A l'instar d'une autre protéine de la famille des peroxydases, la myéloperoxydase humaine, la proséquence de la hTPO agit comme une protéine chaperon interne en facilitant le repliement correct de la protéine. Ces résultats éclairent davantage notre connaissance des mécanismes impliqués dans la maturation de la hTPO et expliquent l'hétérogénéité de la TPO exprimée dans la thyroïde humaine.

Amyloidosis bears many characteristics of orphan diseases. Its diagnosis is difficult and often delayed. The main reasons thereof are its quite various clinical presentation: amyloidosis behaves as a new great masquerader, and the need to get a tissue sample to submit to specific dyes. Although we have been able for a long time to recognize amyloid, its intimate nature has remained quite completely enigmatic until recently. In fact, major advances in this way have appeared only in the last decade and it is now possible to consider the mechanisms of amyloidosis as a multistep phenomenon. Amyloidosis is no more thought only as astorage diseaseof the extracellular space. This archaic viewpoint has shifted to the emerging paradigm of misfolded protein disorders. Amyloid proteins thus appear as a subgroup of misfolded proteins, where misfolding leads to subsequent aggregation. This aggregation may be a generic property of polypeptide chains possibly linked to their common peptide backbone that does not depend on specific amino acid sequences. And, in fact, many proteins can in vitro form amyloid-like aggregates, while in vivo, only 20 amyloid proteins have been so far identified. Although misfolding and aggregation are quite well studied in vitro, the last step of amyloid deposition, i.e. anchorage to the extracellular matrix, can not be so easily approached. Proteoglycans and serum amyloid P component have nevertheless been identified as key elements involved in extracellular deposition of amyloid proteins. These advances have opened new avenues in the therapeutic of amyloid disorders. Current treatment consists of support or replacement of impaired organ function and measures to reduce the production of amyloidogenic precursor proteins. Potential novel therapeutic strategies include stabilisation of the native fold of precursor proteins with targeted small molecules, reversion of misfolded proteins to their native state withbeta-sheet breakers, inhibition of amyloid fibril propagation and enhancement of amyloid clearance either through immunotherapy or by reducing the stability of deposits through depletion of serum amyloid P component, and breaking the anchorage to the extracellular matrix with glycosaminoglycan analogs.

International audience; The partial unfolding or alternative folding of a class of polypeptides is at the origin of fascinating events in living cells. In their non-native conformation, these constitutive polypeptides called prions are at the origin of a protein-based structural heredity. These polypeptides are closely associated to a class of fatal neurodegenerative illnesses in mammals and to the emergence and propagation of phenotypic traits in baker's yeasts. The structural transition from the correctly folded, native form of a prion protein to a persistent misfolded form that ultimately may cause cell death or the transmission of phenotypic traits is not yet fully understood. The mechanistic models accounting for this structure-based mode of inheritance and the extent of partial unfolding of prions or their alternative folding and the subsequent aggregation process are developed and discussed. Finally, the potential regulation of prion propagation by molecular chaperones is presented.; Le dépliement partiel ou le repliement alternatif d’une classe de polypeptides sont à l’origine d’événements fascinants dans la cellule : dans une conformation non native, ces polypeptides constitutifs, appelés prions, sont le vecteur d’une hérédité structurale. Ces polypeptides sont responsables d’une classe de maladies neurodégénératives chez les mammifères, et de l’apparition et la propagation de caractères phénotypiques chez la levure de boulanger. La nature du changement de conformation à l’origine de l’acquisition de propriétés infectieuses par un prion correctement replié, c’est-à-dire natif, n’est pas encore totalement connue. Les modèles mécanistiques qui peuvent rendre compte de cette hérédité structurale, ainsi que l’étendue du dépliement partiel ou du repliement alternatif des prions et leur agrégation en oligomères de masse moléculaire élevée sont présentés et discutés dans cet article. Les mécanismes potentiels de régulation de la propagation des prions par les chaperons moléculaires sont également développés.

A protein's three-dimensional structure is encoded in its amino acid sequence. Thefolding problemconsists in predicting one based on the other. This classic problem of molecular biology has seen important steps forward in recent years. The raw power of today's computers, along with the mobilization of thousands of internauts, have allowed several small proteins to be literally folded up in a computer, through simulations. Moreover, international programs for structural genomics aim to determine the experimental structures of hundreds of proteins in several organisms, and to model the others by homology to known structures. This will lead to a nearly-complete map of the protein structure universe, shedding light on the past evolution and current functions of today's proteins, and suggesting new targets for therapeutic strategies.

Protein folding is a topic of fundamental interest since it concerns the mechanisms by which the genetic information is translated into the three-dimensional and functional structure of proteins. In these post-genomic times, the knowledge of the fundamental principles is required in the exploitation of the information contained in the increasing number of sequenced genomes. Protein folding also has a practical application in the understanding of different pathologies associated with protein misfolding and aggregation. Significant advances have been made ranging from the Anfinsen postulate to the "new view" which describes the folding process in terms of an energy landscape. These insights arise from both theoretical and experimental studies. Unravelling the mechanisms of protein folding represents one of the most challenging problems to day. This is an extremely active field of research involving aspects of biology, chemistry, biochemistry, computer science and physics.

The biotechnology of recombinant protein production is now entering its most advanced stage, and the growth of industrial protein pharmaceuticals provides solid proof of this evolution. However, the systematic conversion of genetic information into a biologically active protein is constantly confronted by the fundamental problem of protein folding in cells, and many recombinant proteins are not produced in their native state. Instead, they aggregate into a biologically inactive state. Although this aggregation reaction has some practical advantages, in vitro renaturation of recombinant proteins, after solubilization of cellular aggregates, is still an empiric and random process. Thus, it is better to control cellular expression conditions to minimize this problem inside the cells. The most attractive approach is certainly the development of high throughput genetic screens to monitor efficient protein folding.

This work is devoted to the study of photolysis of carbonmonoxy myoglobin (MbCO) followed by time resolved circular dichroism (TRCD). Conformational changes that occur in myoglobin are known to play an important physiological role as a model of the trigger of the a! llosteric transformation which takes place in hemoglobin. Upon! ligand dissociation, the heme undergoes an ultrafast doming which propagates along the whole protein through the proximal hisitidine. Experimental measurement of time resolved CD have been carried out in this system. The tricky point was to get rid of the artifact that occurs in such an experiment. A model calculation of CD in myoglobin based on the polarisability theory evidences the key role of the proximal hisitidine. The striking result of this work is a 100 picoseconds dynamics which we assign to a motion of the proximal histidine. A new UV laser source has been built up. The main goal is to follow the first steps of the folding of small polypeptides performing TRCD at 220 nm. Preliminary results are shown., L'objet de ce travail de thèse est l'étude de la photodissociation de la carboxymyoglobine (MbCO) par dichroïsme circulaire résolu temporellement (TRCD). La myoglobine (Mb) est une protéine responsable du stockage de l'oxygène dans les muscles de l'organisme. Lorsque le complexe MbCO absorbe un photon visible, il y a photodissociation, le CO se détache et quitte la protéine. Il s'agit donc de mesurer le dichroïsme circulaire de la myoglobine juste après la photodissociation, afin de pouvoir remonter aux changements de structure ultra rapides de la protéine. D'un point de vue expérimental, la difficulté de ce travail résidait dans la maîtrise des nombreux artefacts d'une telle expérience. D'un point de vue théorique, un calcul basé sur la théorie de la polarisabilité a permis de montre! r que le CD était sensible essentiellement aux mouvements de l'histidine proximale, résidu clef dans la compréhension de l'effet allostérique. Le résultat marquant de cette étude a donc été la mise en évidence d'une dynamique temporelle de 100 ps, attribuée à un mouvement de l'histidine proximale. Une nouvelle source laser a également été développée dans le but de faire des expériences de TRCD dans l'ultraviolet. L'objectif est de pouvoir suivre à terme la dynamique de repliement des protéines. Des résultats préliminaires ont été obtenus.

Prion diseases form a group of fatal neurodegenerative disorders including Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in animals. All of which are characterized by the accumulation of abnormally folded isoform of the cellular prion protein (PrP(C)), denoted PrP(Sc), which is the major component of infectious prion diseases. The function of PrP(C) remains elusive. Its amino-terminal region contains a repeated five octapeptide domain that binds copper. The protein is believed to display a superoxide dismutase like activity, and hence a possible protective function against oxidative stress. In this review, relationship between PrP, copper and oxidative stress was analysed. Thus, metal ions and oxidative stress would play an essential role in the pathogenesis of prion diseases and represent important targets for future therapeutic targets or a novel diagnostic marker.

Huntington's disease is an hereditary dominant neurodegenerative disorder clinically characterised by progressive dyskinesia, cognitive decline and psychiatric disturbances. One decade after the identification of the gene whose mutation is responsible for the disease, this pathology remains incurable. However, major insights into early cellular and molecular basis of Huntington's disease have arisen from transgenic models. Transcriptional dysregulation, abnormal degradation of misfolded proteins as well as excitotoxic processes and mitochondrial dysfunction are involved in Huntington's disease. The present review discusses the recent insights gained from mouse and Drosophila models towards the understanding of pathogenesis and the development of new therapeutic tools.

Parkinson's disease is characterized by the progressive and selective loss of the dopaminergic neurons in the substantia nigra and the presence of ubiquitinated protein inclusions termed Lewy bodies. In the past six years, four genes involved in rare inherited forms of Parkinson's disease have been identified: mutations in the alpha-synuclein and ubiquitin carboxyterminal hydrolase L1 genes (UCH-L1) cause autosomal dominant forms, whereas mutations in the Parkin and DJ-1 genes are responsible for autosomal recessive forms of the disease. A toxic gain of function related to the ability of alpha-synuclein to assemble into insoluble amyloid fibrils may underlie neuronal cell death in parkinsonism due to alpha-synuclein gene mutations. In contrast, loss of protein function appears to be the cause of the disease in parkinsonism due to mutations in the genes encoding Parkin and UCH-L1, which are key enzymes of the ubiquitin-proteasome pathway. The presence of alpha-synuclein, Parkin and UCH-L1 in Lewy bodies suggests that dysfunction of pathways involved in protein folding and degradation is not only involved in the pathogenesis of familial Parkinson's disease, but could also play a role in the frequent sporadic form of the disease (idiopathic Parkinson's disease).

Haemoglobins from unicellular organisms, plants or animals, share a common structure, which results from the folding, around the heme group, of a polypeptide chain made from 6-8 helices. Nowadays, deciphering the genome of several species allows one to draw the evolutionary tree of this protein going back to 1800 millions of years, at a time when oxygen began to accumulate in the atmosphere. This permits to follow the evolution of the ancestral gene and of its product. It is likely that, only in complex multicellular species, transport and storage of oxygen became the main physiological function of this molecule. In addition, in unicellular organisms and small invertebrates, it is likely that the main function of this protein was to protect the organism from the toxic effect of O2, CO and NO*. The very high oxygen affinity of these molecules, leading them to act rather as a scavenger as an oxygen carrier, supports this hypothesis. Haemoglobins from microorganisms, which may probably be the closest vestiges to the ancestral molecules, are divided into three families. The first one is made from flavohaemoglobins, a group of chimerical proteins carrying a globin domain and an oxido-reduction FAD-dependant domain. The second corresponds to truncated haemoglobins, which are hexacoordinated with very high oxygen-affinity molecules, 20-40 residues shorter than classical haemoglobins. The third group is made from bacterial haemoglobins such as that of Vitreoscilla. Some specific structural arrangements in the region surrounding the heme are cause of their high oxygen affinity. In plants, two types of haemoglobins are present (non-symbiotic and symbiotic), that arose from duplication of an ancestral vegetal gene. Non-symbiotic haemoglobins, which are probably the oldest, are scarcely distributed within tissues having high energetic consumption. Conversely, symbiotic haemoglobins (also named leghaemoglobins) are present at a high concentration (mM) mostly in the rhizomes of legumes, where they are involved in nitrogen metabolism. In some species, haemoglobin was proposed to be an oxygen sensor bringing to the organism information to adjust metabolism or biosynthesis to the oxygen requirement. Elsewhere haemoglobin may act as final electron acceptors in oxido-reduction pathways. Evolution of haemoglobin in invertebrates followed a large variety of scenarios. Some surprising functions as sulphide acquisition in invertebrates living near hydrothermal vents, or a role in the phototrophism of worm need to be mentioned. In invertebrates, the size of haemoglobin varies from monomers to giant molecules associating up to 144 subunits, while in vertebrates it is always a tetramer. In some species, several haemoglobins, with completely different structure and function, may coexist. This demonstrates how hazardous may be to extrapolate the function of a protein from only structural data.

Gaucher disease is a lysosomal storage disorder caused by a deficiency in glucocerebrosidase which cleaves the beta-glucosidic linkage of glucosylceramide, a normal intermediate in glycolipid metabolism. Glucocerebrosidase belongs to the clan GH-A of glycoside hydrolases, a large group of enzymes which function with retention of the anomeric configuration at the hydrolysis site. Accurate three-dimensional (3D) structure data for glucocerebrosidase should help to better understand the molecular bases of Gaucher disease. As such 3D structure data were not available, we used the two-dimensional hydrophobic cluster analysis (HCA) method to make structure predictions for the catalytic domains of clan GH-A glycoside hydrolases. We found that all the enzymes of clan GH-A may share a similar catalytic domain consisting of an (alpha/beta)8 barrel with the critical acid/base and nucleophile residues located at the C-terminal ends of strands beta 4 and beta 7, respectively. In the case of glucocerebrosidase, Glu 235 was predicted to be the putative acid/base catalyst whereas the nucleophile was located at Glu 340. Next, in order to obtain experimental evidence supporting these HCA-based predictions, we used retroviral vectors to express, in murine null cells, E235A and E340A mutant proteins, in which alanine residues unable to participate in the enzymatic reaction replace the presumed critical glutamic acid residues. Both mutants were found to be catalytically inactive although they were correctly folded/processed and sorted to the lysosome. Thus, Glu 235 and Glu 340 do indeed play key roles in the active site of human glucocerebrosidase as predicted by the HCA analysis. In a broader perspective, our work points out that bioinformatics approaches may be highly useful for generating structure-function predictions based on sequence-structure interrelationships, especially in the context of a rapid increase in protein sequence information through genome sequencing.

Rabies virus (VR) glycoprotein (G) forms spicules at the surface of virions. These spicules have the shape of a globular mass at the tip of a rod. They ensure the attachment of the VR to its target cell and, following the endocytosis of the VR, the protonation of G causes conformational rearrangements which cause the membrane of the virus to merge with that of the cell.The folding of G ectodomain was studied along two axes. The first consisted in characterizing the effect of the transmembrane anchoring domain (DTM) on the structure of the ectodomain of G during its biosynthesis. Different types of membrane anchors have been attached to the ectodomain and ectodomain structure has been probed using monoclonal antibodies. This has allowed us to show that the DTM ensures an optimal distance between the ectodomain and the membrane, otherwise, the protein folds into an alternative form. We thus suggest that a segment of G ectodomain interacts with the membrane and that this interaction is necessary for native folding.In addition, motifs whose mutation also causes alternative folding have been identified in the juxtamembrane region (His-Pro / 397-398 and Asp-Glu-Ala-Glu-Asp / 410-414). The second axis of the structural study of G consisted in analyzing the structure of two peptides corresponding to this region, produced in bacteria, using different spectroscopic techniques. This study has shown that their structure depends on external factors. It could be another region of the protein and / or the membrane.In the third part, a test allowing to follow the fusion of transfected cells was developed. This has supported the functional characterization of all the mutants produced and to specify the role of different domains of G in the membrane fusion process., La glycoprotéine (G) du virus rabique (VR) forme des spicules à la surface des virions. Ces spicules ont la forme d'une masse globulaire portée par une tige. Elles assurent l'attachement du VR à sa cellule cible et, à la suite de l'endocytose du VR, la protonation de G entraîne des réarrangements conformationnels qui provoquent la fusion de la membrane du virus avec celle de la cellule.Le repliement de l'ectodomaine de G a été étudié selon deux axes. Le premier a consisté à caractériser l'effet du domaine d'ancrage transmembranaire (DTM) sur la structure de l'ectodomaine de G lors de sa biosynthèse. Différents types d'ancrage à la membrane ont été attachés à l'ectodomaine et la structure de celui-ci a été caractérisée à l'aide d'anticorps monoclonaux. Cela nous a permis de montrer que le rôle du DTM est d'assurer une distance optimale entre l'ectodomaine et la membrane, faute de quoi, la protéine se replie sous une forme alternative. Nous en avons déduit qu'un segment de l'ectodomaine de G interagit avec la membrane et que cette interaction est nécessaire pour l'acquisition de sa conformation native.Par ailleurs des motifs dont la mutation provoque aussi un repliement alternatif ont été identifiés dans la région juxtamembranaire (His-Pro/397-398 et Asp-Glu-Ala-Glu-Asp/410-414). Le deuxième axe de l'étude structurale de G a consisté à analyser la structure de deux peptides correspondant à cette région, produits en bactéries, à l'aide de différentes techniques spectroscopiques. Cette étude a montré que leur structure dépend de facteurs extérieurs. Il pourrait s'agir d'une autre région de la protéine et / ou de la membrane.Dans une troisième partie, un test permettant de suivre la fusion de cellules transfectées a été mis au point. Ceci nous a permis de caractériser de façon fonctionnelle l'ensemble des mutants réalisés et de préciser le rôle de différents domaines de G dans la fusion membranaire qu'elle induit.

Elastin is the main protein of elastic fibers and confers the property of elastic recoil to the tissues such as arteries, lung, elastic cartilage,... Elastin synthesis goes through several steps: gene transcription, alternative splicing of pre-mRNA, mRNA translation, hydroxylation of some proline residues of the newly synthesized protein-tropoelastin-, association of with a 67 kDa chaperone protein, secretion of tropoelastin molecules in the extracellular space, and their deposition on the microfibrillar scaffold which contains fibrillin 1, fibrillin 2, MAGP 1 and MAGP 2,.... After the synthesis of cross-links-lysinonorleucine, desmosine, isodesmosine-, elastin becomes insoluble and elastic. The elastogenic pathway is regulated at many levels. The most recently described regulatory mechanism of elastin synthesis is the control of elastin mRNA stability. Elastogenesis is well controlled during development and aging but remains responsive to external factors such as soluble compounds-cytokines, vitamins, hormones,...- and hemodynamic stress. In order to ensure its function, both quantity and quality of elastin should be and should remain optimal in elastic tissues.

Formation of the viral envelope is an important step in the morphogenesis of enveloped viruses. Our data on the formation of hepatitis C virus (HCV) envelope indicate that endoplasmic reticulum (ER) chaperones play a role in the assembly of HCV envelope proteins (E1 and E2). We have shown that these glycoproteins interact with BiP, calreticulin and calnexin. However, among these chaperones, only calnexin is involved in the productive assembly of E1E2 complex. The other two chaperones interact with misfolded aggregates containing E1 and E2. Folding of HCV glycoproteins occurs in the context of intermediate complexes involving E1, E2 and calnexin. As soon as E1E2 heterodimers are properly folded, they separate from calnexin but don't leave the ER compartment.