FrpC protein produced by Neisseria meningitidis in a human host belongs to the family of bacterial RTX toxins due to the presence of RTX domain. FrpC possesses a calcium-dependent auto-catalytic cleavage activity which is localized within its 177 amino-acids long segment Self-Processing Module (SPM). As the SPM is naturally intrinsically disordered protein without bound Ca2+, the calcium binding is crucial for SPM folding which is followed by the auto-catalytic processing. The elucidation of the SPM structure may be the key step for understanding of enzymatic and biological function. The structure of folded SPM itself can be characterized only with difficulties due to the presence of flexible loop according to preliminary NMR data. The subject of this work is the description of SPM using fluorescence methods, characterization of ions binding to SPM and structural changes occurring during Ca2+ binding. In this work, the ion binding properties of SPM segment and its ion-induced folding was characterized. It was found that the dissociation constant kD of 17 μM coincided with the folding of SPM into the native calcium-bound state which occurs in the concentration range between 1 and 20 μM Ca2+. In the attempt to characterize the structure of ion binding site, the fully active single tryptophan mutants...

Legionella pneumophila est responsable d'une forme de pneumonie, la legionellose ou de maladie du légionnaire. Entre 2012 et 2015, les cas annuels ont grimpé de 5848 à 7069 en Europe, la France, l’Allemagne, l’Italie et l’Espagne correspondant à 69% du total. De façon inquiétante, la mortalité était de 8,2% faisant de cette maladie un réel enjeu de santé publique. Un facteur de virulence produit par cette bactérie est la protéine RtxA (~700 kDa) de la famille des protéines RTX (Repeats in ToXin) sécrétée via un système de sécrétion de type 1. Dans ce travail, in vitro, la protéase périplasmique LapG clive la partie N-terminale de RtxA au sein d'un motif di-alanine (position 108-109). La construction de mutants déficients dans l’expression de LapG et LapD a révélé une localisation de RtxA sous le contrôle de ces deux protéines, mécanisme semblable au modèle LapA décrit chez P. fluorescens. Un mutant lapG maintient RtxA à la surface de cellules, à l’opposé d’un mutant ?lapD. Nous avons identifié des systèmes homologues T1SS/LapDG dans de nombreuses espèces Legionella ainsi que d’autres gammaproteobactéries. Concernant la virulence de L. pneumophila, les mutants déficients pour le T1SS (lssBD/tolC) étaient plus altérés dans leur virulence que des mutants du système LapDG. Nous avons également montré, grâce à des expériences de compétition, que L. pneumophila semble cibler les cellules hôtes via la protéine RtxA. L’utilisation d’anticorps spécifiques anti-RtxA nous a permis de détecter RtxA à la surface des cellules hôtes, mais aussi de réduire de la virulence de L. pneumophila, suggérant un rôle important de RtxA lors du processus d’infection, bien que non limitant / Legionella pneumophila is the causative agent of a form of pneumonia called legionellosis or Legionnaires’ disease. Between 2012 and 2015, the reported European cases of legionellosis increased from 5,848 to 7,069 cases per year where France, Germany, Italy and Spain accounted for 69% of the reported cases. Worryingly, the case fatality of incidents was 8.2% making this disease a considerable health concern. One virulence factor produced by this bacterium is a large protein (~700 kDa) belonging to the RTX (Repeats in ToXin) family called RtxA secreted by the type 1 secretion system. The hereby work reveals that, in vitro, LapG periplasmic protease cleaves RtxA N-terminus in the middle of a di-alanine motif (a.a. 108-109). We also show using lapG and lapD mutant strains, that RtxA release is controlled by these two proteins similar to Pseudomonas fluorescenes LapA. We observed that a strain lacking LapG protease maintains RtxA on the cell surface, while a strain lacking LapD does not exhibit cell surface RtxA. Interestingly, we identified the presence of homologous potential T1SS/LapDG systems in many Legionella species and other Gammaproteobacteria. Regarding L. pneumophila virulence, our work showed that mutants for L. pneumophila T1SS (lssBD/tolC) were more disruptive to its virulence than lapG/lapD mutants. We also hypothesize, by challenging infection, that L. pneumophila might be actively targeting its host via RtxA. Additionally, by observing rtxA mutants as well as detecting RtxA on host surface briefly after inoculation and attenuating virulence by using anti RtxA antibodies, we assume an important but not limiting role for this protein in the infection process