Blockers of VacA provide insights into the structure of the pore.
The cytotoxic effects of the Helicobacter pylori toxin VacA, an important etiogenic factor in human gastric diseases, are due to its ability to form anion-selective pores in target cell membranes. We have studied the inhibition of channel activity by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), representatives of two popular classes of chloride channel blockers, to gain information on the mechanism of blocking and on the unknown structure of the VacA pore. The data indicate that both compounds produce a fast block by binding to separate but mutually exclusive sites within the channel lumen. DIDS binds close to the pore opening on the side of protein insertion, whereas NPPB blocks at a position in the opposite half of the channel. Although DIDS reaches the blocking site by traveling along the lumen, inhibition by NPPB appears to involve mainly partition of the compound into the membrane, voltage-independent diffusion from it to the inhibitory position, and voltage-dependent exit. The data are consistent with a pore that can be more easily entered from the side of protein insertion than from the opposite end.
Censiglio Nazionale delle Ricerche, Centro Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, Padova, Italy.
F
F
Tombola
G
G
Del Giudice
E
E
Papini
M
M
Zoratti
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000502:physiology*; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D004553:Electric Conductivity; D016480:Helicobacter pylori / Q000472:pathogenicity / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008958:Models, Molecular; D009579:Nitrobenzoates / Q000494:pharmacology*; D011487:Protein Conformation; D013272:Stomach Diseases / Q000382:microbiology
D001426:Bacterial Proteins; D018118:Chloride Channels; D008051:Lipid Bilayers; D009579:Nitrobenzoates; C074689:VacA protein, Helicobacter pylori; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid