Structural characterization of Cag proteins from the Pathogenicity Island of Helicobacter pylori

Helicobacter pylori chronically infects the gastric mucosa of millions of people annually worldwide: it has been estimated that over 50 % of the world population carries this infection. H. pylori has been associated with the development of several diseases, like chronic gastritis, gastric and duodenal ulcer, gastric adenocarcinoma and mucosa-associated lymphoma. H. pylori contains a foreign DNA region of about 47 kb, called cag (cytotoxin associated genes) Pathogenicity Island (cag-PAI), cause the most severe form of virulence. Some of the cag-PAI genes encode proteins with homology to components of the plant pathogen Agrobacterium tumefaciens VirB/D4 system, which is considered the prototype of bacterial type IV secretion systems (TFSSs). T4SSs are multi-subunit machines that can deliver proteins and/or DNA into host cells and thereby influence host cell functions. In particular, the cag TFSS translocates the CagA effector protein into host epithelial cells. After entering the host cell, CagA induces cellular modifications, such as elongation and spreading of host cells. The aim of this thesis is to determine the three-dimensional structure of some of the proteins encoded by the cag-PAI, a task that will allow to elucidate the function and the organization of the entire T4SS of such a relevant pathogenic bacterium. To date, the three dimensional structure of only two proteins of cag-PAI are known: one is Cagα, an ATPase located at the level of the inner membrane, and the other one is CagZ, a protein essential for the translocation of CagA, whose three- dimensional crystal structure has been determined by our group. In particular, we focalized our attention on four Cag proteins (CagA, CagD, CagS and CagV) and on another protein called HpYbgC that does not belong to the cag-PAI but that has been found to be directly involved into the interaction with the CagA toxin. The research described in this thesis was mostly carried out at the Department of Chemistry, University of Padua and Venetian Institute of Molecular Medicine (VIMM), Padua