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Induction of Lipid Flip-Flop by Colicin E1 – a Hallmark of Proteolipidic Pore Formation in Liposome Membranes

A. A. Sobko1*, S. I. Kovalchuk2, E. A. Kotova1, and Y. N. Antonenko1

1Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia; fax: (495) 939-3181; E-mail: sobko@genebee.msu.ru

2Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, 117871 Moscow, Russia; E-mail: xerx222@gmail.com

* To whom correspondence should be addressed.

Received July 10, 2009; Revision received September 3, 2009
The addition of the channel-forming domain of colicin E1 to liposomes elicited the transmembrane diffusion (flip-flop) of lipids concomitant to the release of the fluorescent dye from liposomes. Good correlation was found between kinetic and concentration dependences of the two processes. Both the liposome leakage and the lipid flip-flop were stimulated upon alkalinization of the buffer solution after colicin binding at acidic pH. These results in combination with the analysis of the data on colicin binding to liposomes provide evidence in favor of the validity of the toroidal (proteolipidic) pore model as the mechanism of colicin channel formation.
KEY WORDS: colicin, ion channel, liposome leakage, proteolipidic pore, flip-flop, fluorescence quenching

DOI: 10.1134/S0006297910060076