Protein subassemblies of the Helicobacter pylori Cag type IV secretion system revealed by localization and interaction studies.

Type IV secretion systems are possibly the most versatile protein transport systems in gram-negative bacteria, with substrates ranging from small proteins to large nucleoprotein complexes. In many cases, such as the cag pathogenicity island of Helicobacter pylori, genes encoding components of a type IV secretion system have been identified due to their sequence similarities to prototypical systems such as the VirB system of Agrobacterium tumefaciens. The Cag type IV secretion system contains at least 14 essential apparatus components and several substrate translocation and auxiliary factors, but the functions of most components cannot be inferred from their sequences due to the lack of similarities.

Topological analysis of a putative virB8 homologue essential for the cag type IV secretion system in Helicobacter pylori.

The type IV secretion system encoded by the cag pathogenicity island of Helicobacter pylori is recognized as a major virulence determinant, governing the translocation of the CagA protein to eukaryotic cells. Despite the presence of 18 genes within the cag pathogenicity island which are essential for this process, several homologues encoding basic functions of a type IV secretion apparatus, such as a virB8 homologue, are still missing. We show here the presence of conserved VirB8 motifs in the cag-encoded apparatus protein HP530 and demonstrate that this protein adopts in E.

A novel sheathed surface organelle of the Helicobacter pylori cag type IV secretion system.

Type I strains of Helicobacter pylori (Hp) use a type IV secretion system (T4SS), encoded by the cag pathogenicity island (cag-PAI), to deliver the bacterial protein CagA into eukaryotic cells and to induce interleukin-8 secretion. Translocated CagA is activated by tyrosine phosphorylation involving Src-family kinases. The mechanism and structural basis for type IV protein secretion is not well understood.

VirB11 ATPases are dynamic hexameric assemblies: new insights into bacterial type IV secretion.

The coupling of ATP binding/hydrolysis to macromolecular secretion systems is crucial to the pathogenicity of Gram-negative bacteria. We reported previously the structure of the ADP-bound form of the hexameric traffic VirB11 ATPase of the Helicobacter pylori type IV secretion system (named HP0525), and proposed that it functions as a gating molecule at the inner membrane, cycling through closed and open forms regulated by ATP binding/hydrolysis. Here, we combine crystal structures with analytical ultracentrifugation experiments to show that VirB11 ATPases indeed function as dynamic hexameric assemblies.