Acid-induced Dissociation of VacA, the Helicobacter pylori Vacuolating Cytotoxin, Reveals Its Pattern of Assembly (original) (raw)
Article| August 25 1997
*Division of Infectious Diseases, Department of Medicine, Vanderbilt University School of Medicine, and the Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232-2605; ‡Department of Pharmacology, Yale University, New Haven, Connecticut 06510; and §Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
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*Division of Infectious Diseases, Department of Medicine, Vanderbilt University School of Medicine, and the Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232-2605; ‡Department of Pharmacology, Yale University, New Haven, Connecticut 06510; and §Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
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*Division of Infectious Diseases, Department of Medicine, Vanderbilt University School of Medicine, and the Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232-2605; ‡Department of Pharmacology, Yale University, New Haven, Connecticut 06510; and §Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
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Timothy L. Cover, Phyllis I. Hanson, John E. Heuser
*Division of Infectious Diseases, Department of Medicine, Vanderbilt University School of Medicine, and the Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232-2605; ‡Department of Pharmacology, Yale University, New Haven, Connecticut 06510; and §Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
Address all correspondence to Timothy L. Cover, Division of Infectious Diseases, A3310 Medical Center North, Vanderbilt University School of Medicine, Nashville, TN 37232. Tel.: (615) 322-2035. Fax: (615) 343-6160.
This project was supported by U.S. Public Health Service grants GM-29647 (J. Heuser), AI-39657, and R29 DK-45293 (T. Cover) by Human Frontiers Science Program grant RG355/94 (J. Heuser), by the Department of Veterans Affairs (T. Cover), and by a postdoctoral fellowship from the Helen Hay Whitney Foundation (P. Hanson).
Received: March 10 1997
Revision Received: June 17 1997
Online ISSN: 1540-8140
Print ISSN: 0021-9525
J Cell Biol (1997) 138 (4): 759–769.
In this study, we describe the ultrastructural changes associated with acid activation of Helicobacter pylori vacuolating cytotoxin (VacA). Purified VacA molecules imaged by deep-etch electron microscopy form _∼_30-nm hexagonal “flowers,” each composed of an ∼15-nm central ring surrounded by six ∼6-nm globular “petals.” Upon exposure to acidic pH, these oligomeric flowers dissociate into collections of up to 12 teardrop-shaped subunits, each measuring ∼6 × 14 nm. Correspondingly, glycerol density gradient centrifugation shows that at neutral pH VacA sediments at ∼22 S, whereas at acidic pH it dissociates and sediments at ∼5 S. Immunoblot and EM analysis of the 5-S material demonstrates that it represents ∼90-kD monomers with 6 × 14–nm “teardrop” morphology. These data indicate that the intact VacA oligomer consists of 12 ∼90-kD subunits assembled into two interlocked six-membered arrays, overlap of which gives rise to the flower-like appearance. Support for this interpretation comes from EM identification of small numbers of relatively “flat” oligomers composed of six teardrop-shaped subunits, interpreted to be halves of the complete flower. These flat forms adsorb to mica in two different orientations, corresponding to hexameric surfaces that are either exposed or sandwiched inside the dodecamer, respectively. This view of VacA structure differs from a previous model in which the flowers were interpreted to be single layers of six monomers and the flat forms were thought to be proteolysed flowers. Since acidification has been shown to potentiate the cytotoxic effects of VacA, the present results suggest that physical disassembly of the VacA oligomer is an important feature of its activation.
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