Molecular basis of alpha5/beta1 integrin exploitation by the Helicobacter pylori type IV secretion system

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Bacterial pathogens such as Helicobacter pylori, Legionella pneumophila, Brucella suis, Bordetella pertusis or Bartonella henselae have evolved dedicated molecular machines, the Type IV secretion systems (T4SS), to colonise organs and counter-attack and subvert host immune defence systems. H. pylori is a Gram-negative bacterium that colonises the human stomach in half of the world population. It is estimated that 20% of individuals infected during their childhood will develop peptic ulcer disease, while gastric neoplasia will develop in 2-3%. For these reasons, H. pylori was defined as a group 1 carcinogen the by World Health Organization (WHO). Strains associated with the most severe diseases contain the cytotoxin-associated gene cagA. CagA is a unique protein encoded by a gene located in the Cag pathogenicity island (CagPAI). This CagPAI encodes for 28 proteins that assemble a T4SS (cagT4SS) required to deliver CagA into the host cell. After translocation, CagA is tyrosine phosphorylated by host Src kinases and highjacks the signalling system of the cell to provoke tumour apparition. CagA is therefore the major determinant of cancer development during H. pylori infection and is considered the paradigm of bacterial carcinogenesis. The mechanism of injection of CagA by the cagT4SS is still poorly understood. It was found that the T4SS utilises beta1 integrin as a host cell receptor for substrate translocation. The objective of the proposed research program is to elucidate the structural and molecular basis of beta1 integrin utilisation by the H. pylori T4SS complex. Our research initiative builds upon recent exciting developments in our research groups and connects structural studies (X-ray crystallography, SAXS, and EM) with interaction studies and cellular assays. The proposal is based on the current collaborative work performed by three groups that has led to: 1) established protocols for purification of the proteins and interaction studies, 2) high resolution studies of CagA structure and identification of its beta1 integrin binding domain, 3) efficient in vivo assays to monitor the functional relevance of the interactions studied.Our short-term goal is to decipher the molecular and structural details of (1) the interactions between pilus protein components (2) their interactions with the beta1 integrin receptor and (3) to determine the sequence of binding events/activation leading to CagA injection. Our groups have a history of successful collaboration and our expertises are genuinely complementary, hereby ensuring a more complete, integrated vision of the integrin exploitation by H. pylori. Although beta1 integrins appear as a common receptor for many pathogens, no structural information is available concerning the details of these interactions. The long-term objectives are to better understand the molecular mechanisms of bacterial infection and to provide new therapeutic strategies, urgently needed to combat these infections.