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J. Biol. Chem., Vol. 281, Issue 29, 19899-19905, July 21, 2006

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Deoxycholic Acid Blocks Vibrio cholerae OmpT but Not OmpU Porin^*

From the Department of Biology & Biochemistry, University of Houston, Houston, Texas 77204

OmpT and OmpU are general diffusion porins of the human intestinal pathogen Vibrio cholerae. The sole presence of OmpT in the outer membrane sensitizes cells to the bile component deoxycholic acid, and the repression of OmpT in the intestine may play an important role in the adaptation of cells to the host environment. Here we report a novel important functional difference between the two porins, namely the sensitivity to deoxycholic acid. Single channel recordings show that submicellar concentrations of sodium deoxycholate induce time-resolved blocking events of OmpT but are devoid of any effect on OmpU. The effects are dose-, voltage-, and pH-dependent. They are elicited by deoxycholate applied to either side of the membrane, with some asymmetry in the sensitivity. The voltage dependence remains even when deoxycholate is applied symmetrically, indicating that it is intrinsic to the binding site. The pH dependence suggests that the active form is the neutral deoxycholic acid and not the negatively charged species. The results are interpreted as deoxycholic acid acting as an open-channel blocker, which may relate to deoxycholic acid permeation.

Received for publication, March 15, 2006 , and in revised form, April 24, 2006.

^* This work was supported by Grant E-1597 from the Robert A. Welch Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Biology & Biochemistry, University of Houston, 369 Science & Research Bldg. 2, Houston, TX 77204-5001. Tel.: 713-743-2684; Fax: 713-743-2636; E-mail: adelcour{at}uh.edu.

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