Obligate intracellular pathogens must acquire host cell-derived nutrients to facilitate their survival. One such bacterial pathogen, Anaplasma phagocytophilum, replicates within neutrophils and non-phagocytic cells in a bacterial-modified, host cell-derived vacuole. The bacterium exploits host cell vesicular trafficking pathways to route nutrients to its vacuole and utilizes Rab GTPases, guanine nucleotide-dependent, vesicular trafficking regulators, to do so. We previously discovered that the A. phagocytophilum vacuolar membrane is decorated with a specific subset of Rab GTPases - Rab1, Rab4A, Rab10, Rab11, Rab14, Rab22A and Rab35. Rab1 is exclusively found on the endoplasmic reticulum (ER) and thus its localization suggests that the bacterium intercepts the ER. Rab10, which is found on the ER, trans-Golgi and recycling endosomes, localizes to the vacuolar membrane in a guanine nucleotide-independent and bacterial protein synthesis-dependent manner. This suggests that a bacterial-encoded protein is binding to and recruiting Rab10. In this study, we determined that A. phagocytophilum hijacks two very nutrient-rich sources in the secretory pathway - trans-Golgi- and endoplasmic reticulum-derived vesicles. A. phagocytophilum localizes perinuclearly adjacent to the Golgi apparatus during infection. A. phagocytophilum and Anaplasma marginale, an intravacuolar bovine pathogen, also localize near the smooth ER and rough ER in both mammalian and tick host cells. These results are supported by transmission electron microscopy analyses of infected cells. Membrane markers for the rough ER label the peripheries of A. marginale and A. phagocytophilum organisms in both mammalian and tick host cells, which suggests that they are translocated into the pathogen vacuole. Furthermore, membrane markers for trans-Golgi-derived vesicles, including endogenous Rab10, label the periphery of intravacuolar A. phagocytophilum organisms. Markers for the trans-Golgi and the ER co-fractionate with A. phagocytophilum in density gradient centrifugation studies. siRNA knockdown of Rab10 pronouncedly reduces delivery of trans-Golgi markers into the pathogen-occupied vacuole, significantly reduces infection, and impedes bacterial conversion to the bacterium’s dense-cored form. These results suggest that trans-Golgi recruitment is Rab10 dependent and is critical for bacterial development. We identified an outer membrane A. phagocytophilum moonlighting protein, uridine monophosphate kinase that specifically binds GST-Rab10 in affinity chromatography assays and interacts with Rab10 in vivo. We hypothesize that this surface protein is mediating the interaction of the bacteria with intravacuolar trans-Golgi derived vesicles. This interaction could be critical for the delivery of essential nutrients. Taken together, these data suggest that nutritional virulence mechanisms of A. phagocytophilum and A. marginale target the host secretory pathway. Additionally, they suggest a novel mechanism whereby pathogens translocate nutrient rich vesicles into the pathogen vacuole, thus delivering essential nutrients right to their front door.

Stomata are structures in plant epidermis which regulate contact between inner and outer environment of the plant by mediating their stomatal aperture. Many inner and outer signals contribute to the ontogenesis of the stomatal pattern. Guard cells undergo significant change of volume and surface during stomatal movement. This change of surface must be compensated by intracellular trafficking of membrane material because biological membrane has limited elasticity. Most of this trafficking takes place between plasma membrane and endosomal compartments. Complex exocyst is protein complex that ensures proper targeting of secretory vesicles to their destination on the plasma membrane. Function of this complex is essential for many cellular processes that require precise targeting of secretion. Mutation in gene Exo70B1 causes different development of the stomatal pattern. Plants with mutated Exo70B1 differ in stomatal size depending on the cultivation conditions more than wild type plant. Protein EXO70B1 is also directly involved in stomatal dynamics because mutants exo70B1 have retarded stomatal opening in response to light. This direct connection can be observed on the fluorescently labeled protein EXOB1 which significantly changes its localization during stomatal movements. None of these observed phenotypes is...

Monoclonal antibodies are well-established as a therapeutic in the biopharmaceutical market, targeting a variety of diseases and with 79 approved products by the United States Food and Drug Administration in December 2019. Therapeutic monoclonal antibodies are commonly produced as recombinant proteins in mammalian cell lines, due to their capacity of post-translational modifications, most notably glycosylation. Furthermore, an identified bottleneck within the production of recombinant proteins is the translocation of nascent proteins from the cytosol into the lumen of the endoplasmic reticulum. The signal peptide, which is located at the N-terminal of nascent proteins, plays a central role in the process of protein secretion. Several studies have shown that optimization of signal peptides is a crucial step for attempting to achieve increased expression of recombinant antibodies in mammalian systems. The aim of this study was to evaluate the expression of three human recombinant antibodies in Human Embryonic Kidney 293 (HEK293) cells by evaluating 16 different signal peptide combinations, consisting of eight heavy chain (HC) and two light chain (LC) signal peptides. The impact goal was an efficient secretion of recombinant antibodies, and thus lower production cost of recombinant antibodies in HEK293 cells. First, 16 HC and LC signal peptide plasmid constructs were generated for each of the three recombinant antibodies. Thereafter, transient gene expression in HEK293 cells were performed at three independent experiments. Finally, the antibody titers were quantified using Biacore concentration analysis. The produced antibody titers for the three studied recombinant antibodies were highly dependent on the used signal peptides. Interestingly, the evaluated HC and LC signal peptide combinations resulted in 3 times higher and 2 times higher antibody titers compared to the original signal peptides used by the Drug Discovery and Development platform at Science for Life Laboratory, for two of the studied antibodies respectively. The results presented in this report further demonstrates the necessity to evaluate signal peptides in order to achieve increased expression of recombinant antibodies in mammalian systems.

O fator de alcalinização rápida ou RALF (do inglês, Rapid ALkalinization Factor) é um peptídeo hormonal ubíquo que induz a atividade de uma MAP quinase, bem como um aumento rápido do pH extracelular do meio de cultura de células em suspensão. O AtRALF1, uma das 37 isoformas de RALF presentes em Arabidopsis thaliana, é um peptídeo secretado de 5 kDa, que inibe o crescimento radicular e causa uma rápida mobilização de Ca2+ extra e intracelular. Em células eucarióticas, calmodulinas são proteínas bem caracterizadas por mediar a transdução de sinais de Ca2+ intracelular. Entretanto, em várias espécies vegetais incluindo Arabidopsis, também existem relatos de calmodulinas secretadas com funções ainda desconhecidas. Neste trabalho, foi caracterizada a AtCML38, uma proteína de Arabidopsis semelhante a calmodulina e que interage com o peptídeo AtRALF1. Análises in silico e por RT-PCR semi-quantitativo mostram a co-expressão de ambos os genes AtRALF1 e AtCML38 em raízes de plântulas de Arabidopsis. Apesar da ausência de um peptídeo sinal típico na proteína AtCML38, a localização sub-celular demonstra que esta é secretada através da via secretória RE-Golgi. O uso de uma versão truncada da AtCML38, cujos 87 primeiros aminoácidos foram retirados, indicou que o N-terminal é essencial para o seu direcionamento. Por meio de ensaios de complementação fluorescente bimolecular, foi demonstrado que AtCML38 interage com AtRALF1 no apoplasto de folhas de tabaco. Ensaios de pulldown indicam que esta interação é específica e dependente de Ca2+ e do pH. Um mutante por inserção de T-DNA, que não produz a proteína AtCML38 (cml38), mostrou-se insensível ao peptídeo AtRALF1 aplicado exogenamente, e suas raízes cresceram normalmente. Plantas transgênicas de Arabidopsis super-expressando o gene AtRALF1 (35S:AtRALF1) têm um fenótipo semi-anão com pronunciada redução do crescimento radicular. Contudo, quando plantas 35S:AtRALF1 foram cruzadas com o mutante cml38, suas progênies exibiram fenótipo e crescimento radicular normais, apesar do acúmulo do peptídeo AtRALF1. Juntos, os resultados mostram que AtCML38 interage com o peptídeo hormonal AtRALF1, e que a proteína AtCML38 é essencial para inibição do crescimento radicular causado pelo peptídeo. / Rapid alkalinization factor (RALF) is a ubiquitous peptide hormone that induces a MAP kinase and a rapid increase in the pH of the extracellular media of cell suspension cultures. AtRALF1, one of the 37 RALF isoforms of Arabidopsis thaliana, is a secreted peptide of 5 kDa that inhibits root growth and causes a rapid mobilization of extra and intracellular Ca2+. In eukaryotic cells, calmodulin proteins are well-characterized to mediate intracellular Ca2+ signal transduction. Nevertheless, in several plant species including Arabidopsis, there are also reports of calmodulins being secreted with still unknown function. In this work, we characterized the AtCML38, a calmodulin-like protein from Arabidopsis as an AtRALF1-interacting protein. Analyses in silico and semiquantitative RT-PCR show co-expression of both AtCML38 and AtRALF1 genes in roots of Arabidopsis seedlings. Despite the fact that AtCML38 lacks a typical signal peptide, subcellular localization demonstrates that AtCML38 is secreted via the ER-Golgi secretory pathway. A truncated AtCML38, without the first 87 amino acids indicates that the N-terminal is essential for targeting. Through bimolecular fluorescence complementation assays, we showed that AtCML38 protein interacts with AtRALF1 in the apoplast of epidermal cells from tobacco leaves. Pull down assays indicate that this interaction is specific, Ca2+- and pH-dependent. A T-DNA insertion mutant defective in the AtCML38 protein (cml38) was insensitive to exogenously applied AtRALF1 peptide and their roots grow just as the wild type plants. Transgenic Arabidopsis plants overexpressing the AtRALF1 gene (35S:AtRALF1) have a semi-dwarf phenotype with a pronounced reduction in the root growth. However, when 35S:AtRALF1 plants are crossed with the mutant cml38, their progenies are normal looking and exhibit normal root growth in spite of the high accumulation of AtRALF1 peptide. Taken together, the results show that AtCML38 interacts with the peptide hormone AtRALF1 and that the protein AtCML38 is essential for the root growth inhibition caused by the peptide.

O gene MAS1/GAS2, conhecido como \"Magnaporthe Apressoria Specific\", foi identificado como altamente expresso durante a formação do apressório do fungo filamentoso fito patogênico Magnaporthe grisea. Em Aspergillus fumigatus, fungo patogênico oportunista, o gene masA, ortólogo a MAS1/GAS2 foi identificado como upregulated em uma análise transcriptômica exposto a voriconazole e anidulafungina, antifúngicos que afetam a síntese do ergosterol e a parede celular, respectivamente. Em ambos os ortólogos apresentam uma estrutura na região N-terminal da proteína denominada peptídeo sinal o qual neste trabalho foi determinado em uma análise in silico a presença de peptídeo sinal na região N-terminal da proteína. Na caracterização fenotípica de uma linhagem masA - deletada de A. fumigatus não foi identificado alteração estrutural do conidióforo e no seu aspecto macromorfológico. A linhagem masA-deletada é resistente a voriconazol e farnesol, drogas que inibem a síntese de ergosterol e a uma molécula quorum sensing, respectivamente. Ao avaliar o nível de expressão gênica do masA frente a diferentes classes de drogas, foi observado que o gene esta super expresso quando ocorre dano na parede celular, membrana citoplasmática, DNA, inibições na síntese de lipídeos e ácidos graxos e no estresse oxidativo. Na presença de dano na parede celular fúngica causados por anidulafungina, a proteína MasA está localizado na parede celular próximo a ponta da hifa. Adicionalmente, foi capaz de transferir para o meio extra-celular a proteína fusionada a ele, a GFP. Assim, possivelmente MasA participa da via secretória do fungo principalmente em momentos de estresse como o desarranjo da parede celular. A capacidade de secreção natural dos fungos filamentosos tem sido explorada no contexto industrial há décadas. Indicando para este fim, uma possível aplicabilidade para este peptídeo sinal. / The MAS1/GAS2 gene, known as \"Magnaporthe Apressoria Specific\", was identified as highly expressed during the formation of the appressorium phyto pathogenic filamentous fungus Magnaporthe grisea. In Aspergillus fumigatus, opportunistic saprophytic fungus, masA gene orthologous to MAS1/GAS2 was identified as upregulated in a transcriptomic analysis exposed to voriconazole and anidulafungin, antifungals that affect the synthesis of ergosterol and the cell wall, respectively. In both orthologs have a structure at the N-terminus of the protein called signal peptide. During the phenotypic and functional characterization of masA gene in A. fumigatus, was determined on an in silico analysis the presence of signal peptide at the N-terminal region of the protein. In the phenotypic characterization of a strain masA - deleted, no structural change of conidiophores and its macromorfologic aspect was not identified. The characterization masA-deleted strain is resistant to voriconazol and farnesol drugs which inhibit ergosterol synthesis and a quorum sensing molecule, respectively. When evaluating the level of gene expression masA against different class of drugs was observed the super gene is expressed when damage occurs in the cell wall and membrane DNA, the synthesis of lipids and fatty acids, and oxidative stress. In the presence of damage in the fungal cell wall caused by anidulafungin, MasA protein is located near the cell wall and the tip of the hypha and additionally, was able to transfer the protein to the extracellular the protein fused to GFP. Thus, possibly MasA participates in the secretory pathway of the fungus especially in stress of the cell wall. The natural secretion capability of filamentous fungi has been exploited in the industrial context for decades. Indicating for this purpose, a possible applicability for this signal peptide.

O gene MAS1/GAS2, conhecido como \"Magnaporthe Apressoria Specific\", foi identificado como altamente expresso durante a formação do apressório do fungo filamentoso fito patogênico Magnaporthe grisea. Em Aspergillus fumigatus, fungo patogênico oportunista, o gene masA, ortólogo a MAS1/GAS2 foi identificado como upregulated em uma análise transcriptômica exposto a voriconazole e anidulafungina, antifúngicos que afetam a síntese do ergosterol e a parede celular, respectivamente. Em ambos os ortólogos apresentam uma estrutura na região N-terminal da proteína denominada peptídeo sinal o qual neste trabalho foi determinado em uma análise in silico a presença de peptídeo sinal na região N-terminal da proteína. Na caracterização fenotípica de uma linhagem masA - deletada de A. fumigatus não foi identificado alteração estrutural do conidióforo e no seu aspecto macromorfológico. A linhagem masA-deletada é resistente a voriconazol e farnesol, drogas que inibem a síntese de ergosterol e a uma molécula quorum sensing, respectivamente. Ao avaliar o nível de expressão gênica do masA frente a diferentes classes de drogas, foi observado que o gene esta super expresso quando ocorre dano na parede celular, membrana citoplasmática, DNA, inibições na síntese de lipídeos e ácidos graxos e no estresse oxidativo. Na presença de dano na parede celular fúngica causados por anidulafungina, a proteína MasA está localizado na parede celular próximo a ponta da hifa. Adicionalmente, foi capaz de transferir para o meio extra-celular a proteína fusionada a ele, a GFP. Assim, possivelmente MasA participa da via secretória do fungo principalmente em momentos de estresse como o desarranjo da parede celular. A capacidade de secreção natural dos fungos filamentosos tem sido explorada no contexto industrial há décadas. Indicando para este fim, uma possível aplicabilidade para este peptídeo sinal. / The MAS1/GAS2 gene, known as \"Magnaporthe Apressoria Specific\", was identified as highly expressed during the formation of the appressorium phyto pathogenic filamentous fungus Magnaporthe grisea. In Aspergillus fumigatus, opportunistic saprophytic fungus, masA gene orthologous to MAS1/GAS2 was identified as upregulated in a transcriptomic analysis exposed to voriconazole and anidulafungin, antifungals that affect the synthesis of ergosterol and the cell wall, respectively. In both orthologs have a structure at the N-terminus of the protein called signal peptide. During the phenotypic and functional characterization of masA gene in A. fumigatus, was determined on an in silico analysis the presence of signal peptide at the N-terminal region of the protein. In the phenotypic characterization of a strain masA - deleted, no structural change of conidiophores and its macromorfologic aspect was not identified. The characterization masA-deleted strain is resistant to voriconazol and farnesol drugs which inhibit ergosterol synthesis and a quorum sensing molecule, respectively. When evaluating the level of gene expression masA against different class of drugs was observed the super gene is expressed when damage occurs in the cell wall and membrane DNA, the synthesis of lipids and fatty acids, and oxidative stress. In the presence of damage in the fungal cell wall caused by anidulafungin, MasA protein is located near the cell wall and the tip of the hypha and additionally, was able to transfer the protein to the extracellular the protein fused to GFP. Thus, possibly MasA participates in the secretory pathway of the fungus especially in stress of the cell wall. The natural secretion capability of filamentous fungi has been exploited in the industrial context for decades. Indicating for this purpose, a possible applicability for this signal peptide.

O fator de alcalinização rápida ou RALF (do inglês, Rapid ALkalinization Factor) é um peptídeo hormonal ubíquo que induz a atividade de uma MAP quinase, bem como um aumento rápido do pH extracelular do meio de cultura de células em suspensão. O AtRALF1, uma das 37 isoformas de RALF presentes em Arabidopsis thaliana, é um peptídeo secretado de 5 kDa, que inibe o crescimento radicular e causa uma rápida mobilização de Ca2+ extra e intracelular. Em células eucarióticas, calmodulinas são proteínas bem caracterizadas por mediar a transdução de sinais de Ca2+ intracelular. Entretanto, em várias espécies vegetais incluindo Arabidopsis, também existem relatos de calmodulinas secretadas com funções ainda desconhecidas. Neste trabalho, foi caracterizada a AtCML38, uma proteína de Arabidopsis semelhante a calmodulina e que interage com o peptídeo AtRALF1. Análises in silico e por RT-PCR semi-quantitativo mostram a co-expressão de ambos os genes AtRALF1 e AtCML38 em raízes de plântulas de Arabidopsis. Apesar da ausência de um peptídeo sinal típico na proteína AtCML38, a localização sub-celular demonstra que esta é secretada através da via secretória RE-Golgi. O uso de uma versão truncada da AtCML38, cujos 87 primeiros aminoácidos foram retirados, indicou que o N-terminal é essencial para o seu direcionamento. Por meio de ensaios de complementação fluorescente bimolecular, foi demonstrado que AtCML38 interage com AtRALF1 no apoplasto de folhas de tabaco. Ensaios de pulldown indicam que esta interação é específica e dependente de Ca2+ e do pH. Um mutante por inserção de T-DNA, que não produz a proteína AtCML38 (cml38), mostrou-se insensível ao peptídeo AtRALF1 aplicado exogenamente, e suas raízes cresceram normalmente. Plantas transgênicas de Arabidopsis super-expressando o gene AtRALF1 (35S:AtRALF1) têm um fenótipo semi-anão com pronunciada redução do crescimento radicular. Contudo, quando plantas 35S:AtRALF1 foram cruzadas com o mutante cml38, suas progênies exibiram fenótipo e crescimento radicular normais, apesar do acúmulo do peptídeo AtRALF1. Juntos, os resultados mostram que AtCML38 interage com o peptídeo hormonal AtRALF1, e que a proteína AtCML38 é essencial para inibição do crescimento radicular causado pelo peptídeo. / Rapid alkalinization factor (RALF) is a ubiquitous peptide hormone that induces a MAP kinase and a rapid increase in the pH of the extracellular media of cell suspension cultures. AtRALF1, one of the 37 RALF isoforms of Arabidopsis thaliana, is a secreted peptide of 5 kDa that inhibits root growth and causes a rapid mobilization of extra and intracellular Ca2+. In eukaryotic cells, calmodulin proteins are well-characterized to mediate intracellular Ca2+ signal transduction. Nevertheless, in several plant species including Arabidopsis, there are also reports of calmodulins being secreted with still unknown function. In this work, we characterized the AtCML38, a calmodulin-like protein from Arabidopsis as an AtRALF1-interacting protein. Analyses in silico and semiquantitative RT-PCR show co-expression of both AtCML38 and AtRALF1 genes in roots of Arabidopsis seedlings. Despite the fact that AtCML38 lacks a typical signal peptide, subcellular localization demonstrates that AtCML38 is secreted via the ER-Golgi secretory pathway. A truncated AtCML38, without the first 87 amino acids indicates that the N-terminal is essential for targeting. Through bimolecular fluorescence complementation assays, we showed that AtCML38 protein interacts with AtRALF1 in the apoplast of epidermal cells from tobacco leaves. Pull down assays indicate that this interaction is specific, Ca2+- and pH-dependent. A T-DNA insertion mutant defective in the AtCML38 protein (cml38) was insensitive to exogenously applied AtRALF1 peptide and their roots grow just as the wild type plants. Transgenic Arabidopsis plants overexpressing the AtRALF1 gene (35S:AtRALF1) have a semi-dwarf phenotype with a pronounced reduction in the root growth. However, when 35S:AtRALF1 plants are crossed with the mutant cml38, their progenies are normal looking and exhibit normal root growth in spite of the high accumulation of AtRALF1 peptide. Taken together, the results show that AtCML38 interacts with the peptide hormone AtRALF1 and that the protein AtCML38 is essential for the root growth inhibition caused by the peptide.

La voie de sécrétion bactérienne de type V permet l’exportation à la surface cellulaire de protéines dont certaines ont été identifiées comme d’importants facteurs de la pathogénicité bactérienne. Le type V regroupe la sécrétion des autotransporteurs et la sécrétion à deux partenaires (TPS). Les autotransporteurs sont constitués d’un domaine en tonneau β; et d’un domaine passager. L’interaction de l’autotransporteur avec le complexe protéique Bam, dont la pièce centrale est le transporteur BamA, permet l’insertion dans la membrane externe du tonneau β; et la sécrétion du passager. En revanche, la sécrétion à deux partenaires fait intervenir deux protéines, l’une appelée TpsA correspondant à la protéine exportée et l’autre, TpsB, formant un tonneau β qui contrôle le transport à travers la membrane externe. Les protéines TpsB sont spécifiques à leur(s) TpsA associée(s), et font partie de la superfamille des transporteurs Omp85 qui effectuent l’insertion de protéines dans la membrane externe bactérienne comme BamA, et dans celles des organites eucaryotes dont les chloroplastes et les mitochondries. Au cours de mon doctorat, je me suis intéressé à la sécrétion de l’hémagglutinine filamenteuse (FHA), qui est l’adhésine majoritaire de Bordetella pertussis, l’agent étiologique de la coqueluche. Cette adhésine qui permet à la bactérie de coloniser le tractus respiratoire de l’hôte est une protéine TpsA de 220 kD. Elle est très efficacement sécrétée par la voie de sécrétion à deux partenaires grâce à son transporteur spécifique TpsB nommé FhaC. L’étude cristallographique de FhaC a révélé un tonneau β; à 16 brins qui forme un canal dans la membrane externe obstrué par l’hélice-α; amino-terminale, H1, partagée par la majorité des TpsB, et par une boucle de surface, L6, conservée dans la superfamille Omp85. Cette conformation suggère un état au repos dans lequel le canal bouché ne pourrait pas transporter son partenaire. Afin de comprendre comment la FHA transite à l’intérieur du pore, il est donc nécessaire de connaître les changements de conformations que subit FhaC. Durant mon travail de thèse, nous avons apporté une vision plus dynamique de la sécrétion à deux partenaires en utilisant le couple FHA/FhaC comme modèle d’étude. Pour cela nous avons utilisé principalement la Résonance Paramagnétique Electronique (RPE). Cette technique de biophysique permet d’étudier FhaC en solution ou réincorporée dans une bicouche lipidique et de rendre compte de la mobilité à un site donné par l’utilisation de sondes paramagnétiques. Ainsi nous avons pu montrer que FhaC est en équilibre entre plusieurs conformations, avec H1 dans le pore ou du côté périplasmique de FhaC. La présence de la FHA déplace cet équilibre, favorisant ainsi la sortie de l’hélice hors du pore. Nous avons, par ailleurs, pu démontrer expérimentalement que la FHA transitait bien à l’intérieur du pore formé par FhaC et que l’hélice H1 se trouvait alors dans le périplasme. L’étude de la boucle L6 nous a permis de montrer que la mobilité de cette boucle était fortement contrainte à l’intérieur du pore même lors de la reconnaissance avec la FHA. Ce ralentissement de mobilité est lié, en autre, à une interaction avec un résidu d’un motif conservé présent sur le brin β13 qui influence la taille du pore. De manière plus générale, cette étude de la dynamique de FhaC contribue à la compréhension des mécanismes moléculaires de la voie TPS et des transporteurs de la superfamille Omp85. / Type V secretion in bacteria mediates the export to the cell surface of proteins, some of which have been identified as important factors of pathogenicity. Type V includes the secretion of autotransporters and the ‘Two-partner Secretion’ (TPS) pathway. Autotransporters consist of a β barrel domain and a passenger domain. The interaction of autotransporters with the Bam complex, of which the BamA transporter is the central component, allows the insertion of the β; barrel in the outer membrane and the secretion of passenger domain. In contrast, the two-partner secretion involves two proteins, the exported ‘TpsA’ protein and its TpsB partner that controls its transport across the outer membrane. TpsB proteins are specific to their associated TpsA(s) and belong to the superfamily of the Omp85 transporters, which carry out the insertion of proteins into the bacterial outer membrane, like BamA, or in the outer membranes of eukaryotic organelles including chloroplasts and mitochondria. For my PhD work, I have been interested in the secretion of filamentous hemagglutinin (FHA), which is the major adhesin of Bordetella pertussis, the causative agent of whooping cough. This adhesin allows the colonization by this bacterium of its host’s respiratory tract. This protein corresponds to a 220kD TpsA protein efficiently secreted by its specific transporter TpsB named FhaC. Crystallographic studies have revealed that FhaC harbours a 16-stranded β;-barrel occluded by both the N-terminal α;-helix, H1, shared by the majority of TpsB proteins, and by a surface loop, L6, that carries a conserved, hallmark motif of the Omp85 superfamilly. This conformation suggests that FhaC is in a resting state in which the channel does not transport its partner. To understand how the FHA passes through the FhaC pore, it is necessary to address the conformational changes undergone by FhaC. During my thesis work, we provided a more dynamic view of the TPS pathway using the FHA/FhaC couple as study model. For this we used Electron Paramagnetic Resonance (EPR). This biophysical technique allows to study of FhaC in solution or reincorporated into a lipid bilayer and it reports the mobility at specific sites of the protein by using paramagnetic probes. Thus we have shown that FhaC is in equilibrium between multiple conformations, with H1 in the pore or at the periplasmic side of FhaC. The presence of FHA displaces the conformational equilibrium, promoting the exit of the helix going from the pore. We have also experimentally demonstrated that FHA does transit through the pore formed by FhaC while helix H1 is then in the periplasm. The study of the L6 loop enabled us to show that the mobility of this loop is highly constrained in the pore and remains so upon the recognition of FHA. Its slow mobility is linked to an interaction between an invariant L6 residue and a conserved motif present on the β; strand 13 of the barrel. This interaction affects the size of the FhaC pore.More generally, the study of the dynamics of FhaC contributes to the understanding the molecular mechanisms of the TPS pathway and of transporters of the Omp85 superfamily.

No description available.

Cornichon (CNI) proteins are a conserved family of proteins among eukaryotes, from Erv14 in the yeast Saccharomyces cerevisiae to CNI homologs (CNIHs) in mammals and plants. Erv14 functions as a cargo receptor of coat protein complex II (COPII) for protein trafficking from the endoplasmic reticulum (ER) to the Golgi apparatus, en route to their final destinations. By interacting with specific cargo proteins, CNI proteins regulate key steps of embryo polarity in Drosophila, budding in yeast, and synaptic transmission in the mammalian brain. However, we have very limited understanding of plant CNIHs. Positive-strand RNA viruses assemble their viral replication complexes (VRCs) at specific host organelle membranes. With a better understanding of host factors involved in targeting viral replication proteins to the preferred organelles, we expect to block trafficking of viral replication proteins and thus, viral infection, by manipulating the required host proteins. Brome mosaic virus (BMV) is a model of positive-strand RNA viruses and its replication can be recapitulated in yeast. Importantly, BMV replication protein 1a is the only required viral protein to form VRCs at the perinuclear ER membrane in yeast. I demonstrate that Erv14 and COPII coat proteins are required for targeting BMV 1a to the perinuclear ER in yeast, suggesting a novel function of COPII vesicles in protein trafficking to the perinuclear ER membrane and in the BMV VRC formation. As for cellular functions, I show that plant CNIHs complement the defective distribution of BMV 1a in yeast mutant lacking Erv14. Taking advantage of Arabidopsis thaliana knockout mutants and knockdown of gene expression in Nicotiana benthamina, I also discover that CNIHs unexpectedly play crucial roles in pollen development, infection of a bacterial pathogen, and maintenance of ER tubules. I further confirm that CNI proteins are also required for maintaining ER tubules in yeast, suggesting a novel and conserved role in shaping ER morphology. Therefore, these findings indicate the functional diversity and redundancy of CNI proteins in key cellular processes and suggest a novel strategy to control plant pathogenic viruses and bacteria by manipulating plant CNIHs. / Ph. D. / Many cellular proteins play important roles in plant development but unfortunately are hijacked by plant viral, bacterial, and/or fungal pathogens for their infections. Cornichon (CNI) proteins are a conserved family of proteins and a great example that is involved in both plant development and plant pathogen infection. CNI protein was first described in a <i>Drosophila</i> mutant. Only 3% of mutant cells survived, but showed abnormal phenotype in abdominal segmentation with a similar shape of “pickle” during embryo development. Later on, this family of proteins was well studied in yeast and mammals but rarely studied in plants. Erv14, one of CNI proteins in yeast, is a cargo receptor of coat protein complex II (COPII) vesicles that participate in cellular early secretory pathway. COPII vesicles serve as cellular carriers to recruit cargo proteins from the endoplasmic reticulum (ER) membrane and depart for the Golgi apparatus, en route to their final destinations for proper cellular processes. In this dissertation, I have discovered that Erv14 and COPII components are unexpectedly involved in targeting a replication protein of a plant RNA virus to the perinuclear ER membrane, instead of the Golgi apparatus, suggesting a novel function of COPII in targeting proteins to the perinuclear ER. Erv14 has never been shown as involved in viral infection and thus, my work has identified a new host protein required for viral infection. I have further explored the cellular functions of CNI proteins in plants, and found that plant CNI proteins play significant roles in maintaining cellular ER network, supporting normal pollen development, and bacterial pathogen infection. Therefore, plant CNI proteins function similarly as Erv14 to recruit various cargo proteins into COPII vesicles en route to their final destinations for proper cellular processes. These cellullar processes may include, but are not limited to: ER morphology maintenance, pollen development, and plant immune response to pathogen infection. Furthermore, it is possible to develop a novel strategy to make plants resistant to plant viruses and/or bacteria by manipulating plant CNIHs.