PHYSICS OF IONIC CHANNELS AND OTHER PROTEINS WITH AQUEOUS CAVITIES

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Our studies have taken advantage of two strategies. 1) Structural features of ionic channels have been delineated by their reaction to polymers of varied size. 2) The very rapid kinetics of electrical conduction have been monitored through sophisticated physical "noise" analysis to follow rapid events such as binding and unbinding of protons from ionizable sites; to test for the channel-forming capabilities of antibiotics known to perturb cell membrane transport; to relate forces measured between macromolecules to the energies that drive channels between functioning states of different structures. From the kinetics of alpha-toxin channels, it was possible to measure the rate of proton binding and unbinding at ionizable sites within the channel. Alamethicin channels appear to speed up in the presence of water soluble polyethylene glycols (PEGS) and dextrans. Added polymers reduce the probabilities of transition to higher conductance states but do not change channel lifetimes. One can relate the degree of each polymer's exclusion to its radius of gyration and to the radius of the channel pore. Novobiocin, an aromatic nitrogen-containing antibiotic often used as a pharmacological agent to enhance the responses of sodium-specific, amiloride-sensitive nerve fibers to sodium chloride, has been found to form ion channels in lipid membranes. Channels can be used as rapid detectors of individual molecular events, in particular of proton binding to ionizable sites. Polymers of different sizes can be used to gauge channel dimensions.