Structural organization of membrane-inserted hexamers formed by Helicobacter pylori VacA toxin.
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.
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232.
Tasia M
TM
Pyburn
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232.
Nora J
NJ
Foegeding
Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, 37232.
Christian
C
González-Rivera
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232.
Nathan A
NA
McDonald
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232.
Kathleen L
KL
Gould
Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, 37232.|Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, 37232.|Veterans Affairs Tennessee Valley Healthcare System, Nashville, TN, 37212.
Timothy L
TL
Cover
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232. melanie.ohi@vanderbilt.edu.|Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232. melanie.ohi@vanderbilt.edu.
Melanie D
MD
Ohi
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003603:Cytotoxins / Q000378:metabolism; D006367:HeLa Cells; D016480:Helicobacter pylori / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D011487:Protein Conformation; D000072417:Protein Domains; D013329:Structure-Activity Relationship; D014617:Vacuoles / Q000378:metabolism
D001426:Bacterial Proteins; D003603:Cytotoxins; D008051:Lipid Bilayers; D008565:Membrane Proteins; C074689:VacA protein, Helicobacter pylori