The Rab-binding profiles of bacterial virulence factors during infection

Legionella pneumophila, the causative agent of Legionnaire's disease, uses its type IV secretion system to translocate over 300 effector proteins into host cells. These effectors subvert host cell signaling pathways to ensure bacterial proliferation. Despite their importance for pathogenesis, the roles of most of the effectors are yet to be characterized. Key to understanding the function of effectors is the identification of host proteins they bind during infection. We previously developed a novel tandem-affinity purification (TAP) approach using hexahistidine and BirA-specific biotinylation tags for isolating translocated effector complexes from infected cells whose composition were subsequently deciphered by mass spectrometry. Here we further advanced the workflow for the TAP approach and determined the infection-dependent interactomes of the effectors SidM and LidA, which were previously reported to promiscuously bind multiple Rab GTPases in vitro. In this study we defined a stringent subset of Rab GTPases targeted by SidM and LidA during infection, comprising of Rab1A, 1B, 6, and 10; in addition, LidA targets Rab14 and 18. Taken together, this study illustrates the power of this approach to profile the intracellular interactomes of bacterial effectors during infection

Les fidélités et les clientèles en France aux XVIe, XVIIe et XVIIIe siècles

Des problèmes de sémantique et de concordance entre pratique réelle et formules en usage rendent peu facile l'étude des liens de fidélité dans la France de l'Ancien Régime. Distincte de la clientèle comme de la féodalité, la fidélité personnelle comportait des sentiments d'affection et favorisait les relations verticales entre un inférieur, faisant don de soi, et son supérieur, le couvrant de son crédit. Elle liait, entre autres, le roi et ses sujets, le chrétien et son Dieu, le gentilhomme et son protecteur à la cour de France. Les valeurs qui sous-tendaient la fidélité perdirent cependant du terrain devant la montée du jansénisme et du rationalisme au XVlIIe siècle. The study of the bonds of loyalty in ancien régime France is hampered by semantics and the gap which possibly existed between actual practice and expressions used. As distinct from clientage or fealty, this personal loyalty involved feelings of affection and fostered the vertical relations between an inferior and his superior, with the former exchanging his devotion for the latter's protection. It bound, for instance, the king and his subjects, a Christian and his God, a gentleman and his patron at court. With the rise of Jansenism and rationalism in the eighteenth century, however, the values underlying such loyalty began to lose ground

Des phénomènes de répétition à la conceptualisation en histoire

Le but de cette conférence est de mettre en lumière l'erreur que l'on fait d'ordinaire, du point de vue du travail historique, lorsqu'on oppose l'histoire, dont l'objet serait le particulier, l'individuel, etc., aux sciences de la nature, visant elles, à l'universel. Car, en réalité, qu'il s'agisse de la biographie, de l'étude de groupes ou d'une société, l'historien conceptualise à partir d'une foule de phénomènes de répétition. Mais c'est aussi par comparaison et différenciation de phénomènes de répétition qu'il forme des concepts généraux (ordres, castes, classes) permettant de regrouper ou de distinguer des types de hiérarchies sociales, indépendamment du temps ou du lieu. Et ce que l'on peut faire pour les hiérarchies sociales, on peut le faire également pour les monarchies, par exemple, les systèmes politiques ou les systèmes de civilisation. The purpose of this conference is to draw attention to the error which is commonly made, in historical work, of comparing history, the object of which is the particular, the individual, etc., to the natural sciences, which deal with the universal. For in reality, whether we are dealing with biography, the study of groups or that of a society, the historian conceptualizes from a mass of phenomena of repetition. But it is also by comparison and differentiation of phenomena of repetition that he forms general concepts, (orders, castes, classes) which allow him to group and distinguish types of social hierarchies independent of time or of place. And what can be done for social hierarchies may equally well be done for monarchies, for instance, or for political systems, or for systems of civilization

The enteropathogenic Escherichia coli effector NleH inhibits apoptosis induced by Clostridium difficile toxin B

Clostridium difficile is a leading cause of nosocomial infections, causing a spectrum of diseases ranging from diarrhoea to pseudomembranous colitis triggered by a range of virulence factors including C. difficile toxins A (TcdA) and B (TcdB). TcdA and TcdB are monoglucosyltransferases that irreversibly glycosylate small Rho GTPases, inhibiting their ability to interact with their effectors, guanine nucleotide exchange factors, and membrane partners, leading to disruption of downstream signalling pathways and cell death. In addition, TcdB targets the mitochondria, inducing the intrinsic apoptotic pathway resulting in TcdB-mediated apoptosis. Modulation of apoptosis is a common strategy used by infectious agents. Recently, we have shown that the enteropathogenic Escherichia coli (EPEC) type III secretion system effector NleH has a broad-range anti-apoptotic activity. In this study we examined the effects of NleH on cells challenged with TcdB. During infection with wild-type EPEC, NleH inhibited TcdB-induced apoptosis at both low and high toxin concentrations. Transfected nleH1 alone was sufficient to block TcdB-induced cell rounding, nuclear condensation, mitochondrial swelling and lysis, and activation of caspase-3. These results show that NleH acts via a global anti-apoptotic pathway

Human Rhinovirus 16 Causes Golgi Apparatus Fragmentation without Blocking Protein Secretion

The replication of picornaviruses has been described to cause fragmentation of the Golgi apparatus that blocks the secretory pathway. The inhibition of major histocompatibility complex class I upregulation and cytokine, chemokine and interferon secretion may have important implications for host defense. Previous studies have shown that disruption of the secretory pathway can be replicated by expression of individual nonstructural proteins; however the situation with different serotypes of human rhinovirus (HRV) is unclear. The expression of 3A protein from HRV14 or HRV2 did not cause Golgi apparatus disruption or a block in secretion, whereas other studies showed that infection of cells with HRV1A did cause Golgi apparatus disruption which was replicated by the expression of 3A. HRV16 is the serotype most widely used in clinical HRV challenge studies; consequently, to address the issue of Golgi apparatus disruption for HRV16, we have systematically and quantitatively examined the effect of HRV16 on both Golgi apparatus fragmentation and protein secretion in HeLa cells. First, we expressed each individual nonstructural protein and examined their cellular localization and their disruption of endoplasmic reticulum and Golgi apparatus architecture. We quantified their effects on the secretory pathway by measuring secretion of the reporter protein Gaussia luciferase. Finally, we examined the same outcomes following infection of cells with live virus. We demonstrate that expression of HRV16 3A and 3AB and, to a lesser extent, 2B caused dispersal of the Golgi structure, and these three nonstructural proteins also inhibited protein secretion. The infection of cells with HRV16 also caused significant Golgi apparatus dispersal; however, this did not result in the inhibition of protein secretion. IMPORTANCE The ability of replicating picornaviruses to influence the function of the secretory pathway has important implications for host defense. However, there appear to be differences between different members of the family and inconsistent results when comparing infection with live virus to expression of individual nonstructural proteins. We demonstrate that individual nonstructural HRV16 proteins, when expressed in HeLa cells, can both fragment the Golgi apparatus and block secretion, whereas viral infection fragments the Golgi apparatus without blocking secretion. This has major implications for how we interpret mechanistic evidence derived from the expression of single viral proteins