CAMP factor is an extracellular pore-forming toxin secreted by the group B streptococci Streptococcus agalactiae. In conjunction with the action of sphingomyelinase secreted by Staphylococcus aureus, which converts membrane sphingomyline to ceramide, CAMP factor kills susceptible cells by creating holes in them. Since the monomeric or oligomeric structure of CAMP factor is not yet known, no studies on the membrane-penetrating domain of this toxin have been done. In the present study, the interaction of a putative hydrophobic domain between residues T90 and V115 with the target membrane was examined by cysteine-scanning mutagenesis and site-selective fluorescent labeling. The combination of steady state and lifetime fluorescence measurements and collisional quenching experiments with nitroxide labeled fatty acids indicate that residues from T90 to V115 contact the membrane upon binding and oligomerization of CAMP factor on cell membranes. More importantly, all these individual assays indicate that the residues from N104C to F109C insert superficially into the membrane with a β-sheet conformation.

CAMP factor is an extracellular pore-forming toxin secreted by the group B streptococci Streptococcus agalactiae. In conjunction with the action of sphingomyelinase secreted by Staphylococcus aureus, which converts membrane sphingomyline to ceramide, CAMP factor kills susceptible cells by creating holes in them. Since the monomeric or oligomeric structure of CAMP factor is not yet known, no studies on the membrane-penetrating domain of this toxin have been done. In the present study, the interaction of a putative hydrophobic domain between residues T90 and V115 with the target membrane was examined by cysteine-scanning mutagenesis and site-selective fluorescent labeling. The combination of steady state and lifetime fluorescence measurements and collisional quenching experiments with nitroxide labeled fatty acids indicate that residues from T90 to V115 contact the membrane upon binding and oligomerization of CAMP factor on cell membranes. More importantly, all these individual assays indicate that the residues from N104C to F109C insert superficially into the membrane with a β-sheet conformation.

Streptococcus agalactiae CAMP factor is a protein exotoxin that contains 226 amino acid residues and forms oligomeric pores on susceptible cell membranes and liposomes. In this study, fragments of CAMP factor were created and recombinantly expressed to identify functional domains that are involved in membrane binding, oligomerization, and membrane insertion. Altogether, six truncated forms of CAMP factor were created and assayed. CAMP1-113, CAMP1-170, CAMP57-226, and CAMP171-226 showed different levels of hemolytic activity. CAMP1-56 and CAMP114-226 did not show hemolytic activity or oligomerization ability, but showed binding ability. CAMP114-226 inhibited the hemolytic activity of wild-type CAMP factor, most likely through ‘one-sided’ oligomerization. From the comparison of these fragments, it emerges that the region between residues 57 and 113 plays a crucial role in oligomerization and membrane insertion. The high binding efficiency of CAMP114-226 suggests this region has great responsibility on membrane binding. The hemolytically inactive fragments showed higher binding efficiency than some of the active fragments. For the hemolytic fragments, higher binding efficiency gave stronger hemolysis. These findings support that CAMP factor has different functional regions for pore-formation.

Streptococcus agalactiae CAMP factor is a protein exotoxin that contains 226 amino acid residues and forms oligomeric pores on susceptible cell membranes and liposomes. In this study, fragments of CAMP factor were created and recombinantly expressed to identify functional domains that are involved in membrane binding, oligomerization, and membrane insertion. Altogether, six truncated forms of CAMP factor were created and assayed. CAMP1-113, CAMP1-170, CAMP57-226, and CAMP171-226 showed different levels of hemolytic activity. CAMP1-56 and CAMP114-226 did not show hemolytic activity or oligomerization ability, but showed binding ability. CAMP114-226 inhibited the hemolytic activity of wild-type CAMP factor, most likely through ‘one-sided’ oligomerization. From the comparison of these fragments, it emerges that the region between residues 57 and 113 plays a crucial role in oligomerization and membrane insertion. The high binding efficiency of CAMP114-226 suggests this region has great responsibility on membrane binding. The hemolytically inactive fragments showed higher binding efficiency than some of the active fragments. For the hemolytic fragments, higher binding efficiency gave stronger hemolysis. These findings support that CAMP factor has different functional regions for pore-formation.

No description available.

Pseudomonas aeruginosa est un pathogène opportuniste responsable de maladies nosocomiales. Il provoque des infections aiguës ou chroniques en employant conjointement plusieurs facteurs de virulence. Les souches les plus agressives possèdent un système de sécrétion de type III (SST3), injectant des toxines directement dans le cytoplasme des cellules eucaryotes grâce à une nano-aiguille. Récemment, une souche clinique hyper-virulente, appelée CLJ1, a été isolée dans l'unité de soins intensifs de l'hôpital universitaire de Grenoble sur un patient souffrant d'une infection pulmonaire hémorragique. Cette souche ne possède pas les gènes codant pour le SST3 mais sécrète une pore-forming toxin, ExlA, non identifiée auparavant. ExlA est une protéine de 172 kDa, formant des pores de 1,6 nm dans la membrane plasmique de plusieurs types de cellules, à l'exception des érythrocytes. Le pore provoque la rétraction des cellules hôtes et finit par induire la mort de la cellule. Nous avons montré que CLJ1 appartenait à un nouveau clade très divergent des souches classiques de P. aeruginosa, dont les membres possèdent le gène exlA au lieu des gènes codant pour le SST3. Les souches exlA-positives que nous avons collectées dans le monde proviennent d'infections humaines et d'échantillons environnementaux. Leur cytotoxicité, sur diverses cellules humaines et sur un modèle murin d’infection pulmonaire, est corrélée avec les niveaux de sécrétion d'ExlA. En plus de la toxicité membranaire, les souches exlA-positives ont montré des activités protéolytiques élevées envers les VE et E-cadhérines, deux protéines adhésives des jonctions adhérentes requises pour l'intégrité de l'endothélium et de l'épithélium, respectivement. Nous avons démontré que la formation de pores par ExlA dans la membrane eucaryote induisait une entrée massive et rapide de calcium dans le cytosol. Cet afflux de calcium permet la maturation et l'activation d'ADAM10, une protéase eucaryote située à la membrane plasmique. L'activation d’ADAM10 induit le clivage de ses substrats naturels : les VE et E-cadhérines. ExlA fait partie de la même famille de pore forming toxin que ShlA de Serratia marcescens. Nous avons démontré que ShlA utilisait le même mécanisme qu’ExlA pour induire le clivage des cadhérines. En conclusion, les souches bactériennes produisant ExlA ou ShlA détournent un mécanisme naturel de l'hôte pour induire la perte d'intégrité tissulaire. / Pseudomonas aeruginosa is an opportunistic pathogen responsible for nosocomial diseases. It provokes acute or chronic infections due to several virulence factors acting in concert. The most aggressive strains possess a Type III Secretion System (T3SS), injecting toxins directly into the cytoplasm of eukaryotic cells thanks to a nano-needle. Recently, a hyper-virulent clinical strain, called CLJ1, was isolated from a patient suffering of hemorrhagic pulmonary infection, at the intensive care unit of Grenoble University Hospital. This strain lacks a T3SS but secretes a pore-forming toxin, ExlA, not previously identified. ExlA is a 172-kDa protein, forming 1.6-nm pores in the plasma membrane of several cell types, except erythrocytes. The pore causes the retraction of host cells and eventually induces necrotic cell death. We showed that CLJ1 belongs to a recently-discovered and highly divergent clade of P. aeruginosa, whose members possess the exlA gene instead of the genes coding for the T3SS and its effectors. The strains we collected worldwide originate from human infections and environmental samples. Their cytotoxicity on various human cells and mouse models of infection was correlated with ExlA secretion levels. In addition to membrane toxicity, exlA-positive strains displayed high proteolytic activities targeting VE and E-cadherins, two intercellular-junction adhesive proteins required for endothelium and epithelium integrity. We thus investigated the mechanisms of ExlA-induced cadherin cleavage. We demonstrated that ExlA pore formation in the eukaryotic membrane induces a massive and rapid entry of calcium into the cytosol. This calcium influx enables the maturation and activation of ADAM10, an eukaryotic protease located at the cell membrane. ADAM10 activation induces the cleavage of its natural substrates: the VE- and E-cadherins. ExlA is related to other toxins, including ShlA from Serratia marcescens, and altogether they constitute a family of pore-forming toxins with unique properties. We demonstrated that ShlA uses the same mechanism as ExlA to induce the cleavage of the cadherins. In conclusion, exlA- and shlA-positive strains hijack a natural mechanism of the host to induce the loss of tissue integrity.

In this thesis the deployment of a methodological combination of two single molecule techniques, the planar bilayer technique and fluorescence fluctuation spectroscopy, is presented. The newly devised electro-optical setup will serve as a sophisticated model system for electrical excitable biological membranes. The expectation on a combined electro-optical setup is to be able to correlate the function of membrane channels (electrical activity) with its structural properties (fluorescence assays). The thesis is grouped into four chapters: A general introduction, providing the biological and methodological background, is followed by two studies on the application of the electro- optical setup in the field of membrane biophysics. In the first study the electrical and diffusion properties of planar bilayer membranes made of simple and ternary lipid mixtures are characterized. Additionally, the influence of temperature dependent lipid phase separation on the electrical activity of the ion channel gramicidin A is studied. The second study addresses the conformational changes of the pore-forming toxin Colicin A during membrane binding and ion channel formation. Finally, the potentials and the limitation of the presented setup are discussed.

No description available.

The production of membranous vesicles is observed to occur among organisms from all domains of the tree of life spanning prokaryotes (bacteria, archaea) and eukaryotes (plants, animals and fungi). Bacterial release of membrane-derived vesicles (MVs) has been studied most extensively in cases of Gram-negative species and implicating their outer membrane in formation of extracellular MVs. However, recent studies focusing on Gram-positive bacteria have established that they also undergo MV formation. Membrane vesicles are released during normal bacterial growth, they are derived from the bacterial membrane(s) and may function as transporters of different proteins, DNA and RNA to the neighbouring bacteria or to the cells of a mammalian host. The transport of virulence factors in a condensed manner via MVs to the host cells presumably protects these proteins from degradation and, thereby, targets the host cells in a specific manner. The aim of my thesis is to investigate secretion of MV-associated virulence factors and to study interactions of MVs produced by two selected Gram-negative and Gram-positive bacteria, i.e. Vibrio cholerae and Listeria monocytogenes, with eukaryotic host cells. Depending on whether the bacterium acts as an extracellular or intracellular pathogen, MVs may be considered to have specific functions, which may lead to the different outcomes of MV-host interactions. V. cholerae transport systems for virulence factors include the Type VI secretion system and MVs (also referred to as the “Type 0” secretion system). We have identified that the biologically active form of PrtV protease in different V. cholerae serogroups is transported via MVs. PrtV protease is essential for V. cholerae environmental survival and protection from natural predator grazing. We demonstrated that PrtV is primarily translocated via the inner membrane to the periplasmic space, where it undergoes autoproteolysis, and the truncated version of PrtV protein is packaged inside the MVs and released from the surface of bacteria. MV-associated PrtV protease showed a contribution to bacterial resistance towards the antimicrobial peptide LL-37, thereby, enhancing bacterial survival by avoiding this innate immune defense of the host. We also studied another virulence factor of V. cholerae, the pore-forming toxin VCC, which was found to be transported by MVs. MV-associated VCC is biologically active and triggers an autophagic response in the target cells. We suggested that autophagy serves as a cellular defense mechanism against the MV-associated bacterial virulence factor of V. cholerae. Listeria monocytogenes is a Gram-positive intracellular and facultative anaerobic food-borne pathogen causing listeriosis. It causes only sporadic outbreaks in healthy individuals, however, it is dangerous for a fetus or newborn child, and for pregnant and immunocompromised people, leading to a deadly infection in one third of the cases. We have analyzed MVs produced by L. monocytogenes and their interaction with eukaryotic cells. Confocal microscopy analysis showed that MVs are internalized into HeLa and HEK293 cells and are accumulated in lysosomes. Moreover, L. monocytogenes produces MVs inside the host cells and even inside the phagosomes. We found that the major virulence factor of L. monocytogenes, the cholesterol-dependent pore-forming protein listeriolysin O (LLO), is entrapped inside the MVs and resides there in an oxidized inactive state. LLO is known to induce autophagy by making pores in the phagosomal membrane of targeted eukaryotic cells. In our studies, we have shown that MVs effectively abrogated autophagy induced by Torin1, by purified LLO or by another pore-forming toxin from V. cholerae. We also found that MVs promote bacterial intracellular survival inside mouse embryonic fibroblasts. In addition, MVs have been shown to have a strong protective activity against host cell necrosis initiated by pore-forming toxin. Taken together, these findings suggested that in vivo MVs production from L. monocytogenes might be a relevant strategy of bacteria to manipulate host responses and to promote bacterial survival inside the host cells.

Pseudomonas aeruginosa est un pathogène opportuniste responsable d’infections nosocomiales sévères associées à un taux élevé de mortalité. Le système de sécrétion de Type III (SST3) et les effecteurs qu’il injecte sont considérés comme des facteurs de virulence prépondérants de P. aeruginosa. Récemment nous avons caractérisé, un groupe de souches ne possédant pas les gènes du SST3, mais dont la virulence repose sur la sécrétion d’une nouvelle toxine de 172 kDa, nommée Exolysine (ExlA) qui provoque la perméabilisation de la membrane des cellules hôtes. ExlA est sécrétée dans le milieu par une porine de la membrane externe, nommée ExlB, formant ainsi un nouveau système de sécrétion à deux partenaires (TPS), ExlBA. Outre le domaine TPS du coté N-terminal de la protéine, impliqué dans sa sécrétion, ExlA possède différents domaines ; des répétitions hémagglutinines, cinq motifs Arginine-Glycine-Acide Aspartique (RGD) et un domaine C-Terminal faiblement conservé. Des tests de cytotoxicité sur des cellules eucaryotes ont montrés que la délétion du domaine C-terminal abolissait l’activité toxique d’ExlA. En utilisant un modèle de liposomes et différents types de cellules eucaryotes, comme les globules rouges, nous avons démontré qu’ExlA forme des pores membranaires de 1.6 nm. De plus, par un criblage cellulaire à haut-débit d’une banque de mutants obtenus par une mutagenèse de transposition, nous avons montré qu’un facteur bactérien additionnel était requis dans la toxicité d’ExlA. En effet, parmi les 7 400 mutants, nous avons identifiés 3 transposons insérés dans des gènes codant pour le pili de type IV, démontrant ainsi que cet appendice impliqué dans l’adhésion des bactéries participe à la toxicité d’ExlA, en permettant un contact rapproché entre la bactérie et les cellules hôtes. Un criblage de macrophages primaires de souris KO pour différentes protéines impliquées dans la voie de l’activation de l’inflammasome, nous a permis de démontrer que le pore formé par ExlA est responsable de l’activation de la Caspase-1 par l’inflammasome NLRP3 conduisant à la maturation de l’interleukine-1ß. Une étude bio-informatique a révélé la présence de gènes homologues à exlA chez d’autres espèces de Pseudomonas non pathogènes, comme P. putida, P. protegens, P. entomophila. Nous avons montré que ces bactéries environnementales sont aussi capables de provoquer une mort cellulaire dépendante de la Caspase-1. Finalement, un criblage d’une banque de macrophages dont les gènes ont été invalidés par la technologie CRISPR/cas9 a révélé que plusieurs protéines du système immunitaire, indirectement liées à l’activation de la Caspase-1 sont impliquées dans la mort cellulaire médiée par ExlA. De plus, nous avons montré que plusieurs sgRNAs ciblant un microARN, mir-741, était grandement enrichi dans les macrophages ayant résisté à une infection avec ExlA. Mir-741 régule l’expression d’enzymes (St8sIa1 et Agpat5) impliquées dans la voie de biosynthèse des sphingolipides et des glycérophospholipides, suggérant ainsi que l’activité d’ExlA requiert un environnement lipidique particulier. / Pseudomonas aeruginosa is a human opportunistic pathogen responsible for nosocomial infections associated with high mortality. The type III secretion system (T3SS) and T3SS-exported toxins have been considered as key infectivity virulence factors. Our team recently characterized a group of strains lacking T3SS, but employing a new pore-forming toxin of 172 kDa, named Exolysin (ExlA) that provokes cell membrane disruption. In this work we demonstrated that the ExlA secretion requires ExlB, a predicted outer membrane protein encoded in the same operon, showing that ExlA-ExlB define a new active Two-Partner Secretion (TPS) system. In addition to the TPS secretion signals, ExlA harbors several distinct domains, which comprise hemagglutinin domains, five Arginine-Glycine-Aspartic acid (RGD) motifs and a non-conserved C-terminal region lacking any identifiable sequence motifs. Cytotoxic assays showed that the deletion of the C-terminal region abolishes host-cell cytolysis. Using liposomes and eukaryotic cells, including red blood cells, we demonstrated that ExlA forms membrane pores of 1.6 nm. Based on a transposon mutagenesis strategy and a high throughput cellular live-dead screen, we identified additional bacterial factors required for ExlA-mediated cell lysis. Among 7 400 mutants, we identified three transposons inserted in genes encoding components of the Type IV pili, which are adhesive extracellular appendices. Type IV pili probably mediate close contact between bacteria and host cells and facilitate ExlA cytotoxic activity. These findings represent the first example of cooperation between a pore-forming toxin of the TPS family and surface appendages to achieve host cell intoxication. Using mice primary bone marrow macrophages we showed that ExlA pores provoke activation of Caspase-1 via the NLRP3-inflamasomme followed by the maturation of the pro-interleukin-1ß. Mining of microbial genomic databases revealed the presence of exlA-like genes in other Pseudomonas species rarely associated with human infections P. putida, P. protegens and P. entomophila. Interestingly, we showed that these environmental bacteria are also able to provoke Caspase-1 cleavage and pro-inflammatory cell death of macrophages. Finally, genome-wide loss-of-function CRISPR/cas9 RAW library screen revealed that several components of the immune system response, indirectly linked to Caspase-1 are involved in the ExlA-mediated cell lysis. Moreover, we found at least three sgRNAs targeting miRNA, mir-741 were highly enriched in resistant macrophages challenged by ExlA. This miRNA regulates enzymes (St8sIa1 and Agpat5) in the sphingolipids and glycerophololipids biosynthesis pathways, suggesting that ExlA activity may require proper lipid environment.