A model system for studies of specific membrane interactions

A model system for the study of specific membrane interactions mediated by membrane-bound receptors and ligands has been developed using the acetylcholine receptor (AchR) and a-bungarotoxin (aBGT) receptor-ligand pair. Acylation of the native toxin generating mono-palmitoyl- -bungarotoxin (PBGT) has rendered the molecule amphipathic and able to spontaneously insert via the fatty acyl chain into preformed phospholipid vesicles. The physical interaction of PBGT with the phospholipid vesicles in terms of its effect on the thermotropic behavior and fluidity of the lipids and its rotational and lateral mobility on the vesicle surface have been studied extensively. Identification of the site of acylation on the toxin molecule has allowed an analysis of the binding site on the toxin for AchR since vesicles containing PBGT attached to and oriented on their surface were still able to bind specifically with high affinity to AchR enriched membranes. Finally the binding of PBGT vesicles to AchR enriched microsac membranes has been studied with respect to the effect of PBGT valency (density of the ligand on the vesicle surface) on the strength of binding.