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J. Biol. Chem., Vol. 281, Issue 20, 14408-14416, May 19, 2006

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Lipid Dependence of the Channel Properties of a Colicin E1-Lipid Toroidal Pore^*

Alexander A. Sobko, Elena A. Kotova, Yuri N. Antonenko¹, Stanislav D. Zakharov^¶, and William A. Cramer

From the A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119992 Moscow, Russia, the Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, and the ^¶Institute of Basic Problems of Biology, Russian Academy of Sciences, Puschino, Moscow Region 142290, Russia

Colicin E1 belongs to a group of bacteriocins whose cytotoxicity toward Escherichia coli is exerted through formation of ion channels that depolarize the cytoplasmic membrane. The lipid dependence of colicin single-channel conductance demonstrated intimate involvement of lipid in the structure of this channel. The colicin formed "small" conductance 60-picosiemens (pS) channels, with properties similar to those previously characterized, in 1,2-dieicosenoyl-sn-glycero-3-phosphocholine (C20) or thinner membranes, whereas it formed a novel "large" conductance 600-pS state in thicker 1,2-dierucoyl-sn-glycero-3-phosphocholine (C22) bilayers. Both channel states were anion-selective and voltage-gated and displayed a requirement for acidic pH. Lipids having negative spontaneous curvature inhibited the formation of both channels but increased the ratio of open 600 pS to 60 pS conductance states. Different diameters of small and large channels, 12 and 16 Å, were determined from the dependence of single-channel conductance on the size of nonelectrolyte solute probes. Colicin-induced lipid "flip-flop" and the decrease in anion selectivity of the channel in the presence of negatively charged lipids implied a significant contribution of lipid to the structure of the channel, most readily described as toroidal organization of lipid and protein to form the channel pore.

Received for publication, December 22, 2005 , and in revised form, March 3, 2006.

^* This work was supported by National Institutes of Health Fogarty Award TW01235 and Grant GM-18457 (to W. A. C.) and by Russian Foundation for Basic Research Grant 06-04-48523 (to Y. N. A.). 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: Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russia. Fax: 70-95-939-31-81; E-mail: antonen{at}genebee.msu.ru.

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