2Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA; fax: (765) 494-4956; E-mail: firstname.lastname@example.org
3Institute of Basic Problems of Biology, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; fax: (7-496) 779-0532; E-mail: email@example.com
* To whom correspondence should be addressed.
Received June 23, 2005; Revision received September 2, 2005
Based on the model of a toroidal protein-lipid pore, the effect of calcium ions on colicin E1 channel was predicted. In electrophysiological experiments Ca2+ suppressed the activity of colicin E1 channels in membranes formed of diphytanoylphosphatidylglycerol, whereas no desorption of the protein occurred from the membrane surface. The effect of Ca2+ was not observed on membranes formed of diphytanoylphosphatidylcholine. Single-channel measurements revealed that Ca2+-induced reduction of the colicin-induced current across the negatively charged membrane was due to a decrease in the number of open colicin channels and not changes in their properties. In line with the toroidal model, the effect of Ca2+ on the colicin E1 channel-forming activity is explained by alteration of the membrane lipid curvature caused by electrostatic interaction of Ca2+ with negatively charged lipid head groups.
KEY WORDS: bilayer lipid membrane, spontaneous curvature, ionic channels, colicin E1, calcium