Molecular aspects of channel formation and ion transport through membranes

A summary Is presented of theoretlcal studles almlng at a better understandlng of the coupling propertles of polypeptlde a-helical segments. and of their aggregation into bundles of various sizes capable of encloslng channels apt to transport Ions through biological membranes. The molecular aspects are stressed. INTRODUCTION Blologlcal membranes surround the cells and thelr varlous compartments. They malntaln the dlfferent domalns wlthln llmlfs but also allow proper communlcatlon between them when needed. insuring the appropriate In and out flux of molecules and ions. Membranes are essentially made of Ilplds. long hydrocarbon chains (wlth polar heads) packed side-by-slde all along their length. formlng a tail-to-tall double layer wlth all the polar heads on one and the other slde (Fig. 1 ) . Water pola r h eads