Structural organization of membrane‐inserted hexamers formed by Helicobacter pylori VacA toxin. Issue 1 (8th July 2016)

• Record Type: Journal Article
• Authors: Pyburn, Tasia M.; Foegeding, Nora J.; González‐Rivera, Christian; McDonald, Nathan A.; Gould, Kathleen L.; Cover, Timothy L.; Ohi, Melanie D.
• Is Part Of: Molecular microbiology. Volume 102:Issue 1(2016)
• Page Start: 22
• Page End: 36
• Publication Date: 2016-07-08
• Subjects: Molecular microbiology -- Periodicals; 572.829
• DOI: 10.1111/mmi.13443
• Languages: English
• ISSNs: 0950-382X

Abstract

Summary: Helicobacter pylori colonizes the human stomach and is a potential cause of peptic ulceration or gastric adenocarcinoma. H. pylori secretes a pore‐forming toxin known as vacuolating cytotoxin A (VacA). The 88 kDa secreted VacA protein, composed of an N‐terminal p33 domain and a C‐terminal p55 domain, assembles into water‐soluble oligomers. The structural organization of membrane‐bound VacA has not been characterized in any detail and the role(s) of specific VacA domains in membrane binding and insertion are unclear. We show that membrane‐bound VacA organizes into hexameric oligomers. Comparison of the two‐dimensional averages of membrane‐bound and soluble VacA hexamers generated using single particle electron microscopy reveals a structural difference in the central region of the oligomers (corresponding to the p33 domain), suggesting that membrane association triggers a structural change in the p33 domain. Analyses of the isolated p55 domain and VacA variants demonstrate that while the p55 domain can bind membranes, the p33 domain is required for membrane insertion. Surprisingly, neither VacA oligomerization nor the presence of putative transmembrane GXXXG repeats in the p33 domain is required for membrane insertion. These findings provide new insights into the process by which VacA binds and inserts into the lipid bilayer to form membrane channels. Abstract : Helicobacter pylori colonizes the stomach and increases the risk of gastroduodenal disease in infected individuals. H. pylori VacA, a secreted toxin, forms channels in cell membranes and causes alterations in host cells. The vacA genotype of a strain correlates with the risk of H. pylori ‐associated gastric cancer and the various forms of VacA have different activities in vitro . We show that upon binding to membrane, monomeric VacA oligomerizes into membrane‐inserted hexamers. There is a visible structural difference in the pore‐forming domain of VacA when comparing soluble and membrane‐bound hexamers. These results provide important new insights into mechanisms of VacA oligomerization and membrane insertion.