The interactions between lipids and proteins which produce ionic channels are vital physiological processes. We propose to study a very simple model system which can be conveniently manipulated to reveal the forces governing peptide-lipid interactions. This system is the voltage-dependent ion channel induced by alamethicin (and synthetic compounds with similar structures) in lipid bilayers.
Our aims are to understand how voltage, lipid composition of the membrane, and peptide structure interact to produce strongly voltage-dependent channels. We take advantage of a defined system, purified components of natural alamethicin, synthetic derivatives and specific chemical modifications of both lipid and peptide. We are able to synthesize new analogues of alamethicin to test our ideas of how alamethicin monomers associate to form channels. We routinely measure conductivity with a sensitivity capable of resolving single molecular events, use correlation and spectral analysis to characterize high-level conductances, and measure the kinetics and time constants of the conductances induced by variius analougues. More recently, we have begun to apply newly developed techniques for measuring very small changes in membrane capacitance and the gating current due to movement of alamethicin monomers. We are developing an isolated-patch technique for measuring the diffusion coefficient of alamethicin monomers inserted in the membrane by an electric field. These new techniques allow us to study states of the alamethicin molecule not previously accessible to experimental observation. We are using alamethicin as a probe in a number of biological preparations to investigate the nature of the lipid environment seen by native conductance mechanisms and membrane proteins.
Our aim i s to understand the forces which determine the structure and function of membrane proteins, especially voltage-dependent channels, and how these forces may be modified by lipid composition and membrane voltage.
| Woodbury, D J; Hall, J E (1988) Vesicle-membrane fusion. Observation of simultaneous membrane incorporation and content release. Biophys J 54:345-9 |
