Membrane lipid response to clathrin coat protein determined by infrared spectroscopy. Possible involvement in coated vesicle formation

Clathrin, the major structural protein associated with both coated pits and coated vesicles, has been implicated in the dynamics of various endocytotic processes. In an attempt to define the mechanisms involved in the transition from uncoated membranes to clathrin-coated pits and then coated vesicles, we investigated by infrared spectroscopy the lipid perturbations arising from the interactions of the clathrin coat with the bilayers of intact membrane assemblies. A comparison of the lipid acyl chain symmetric methylene stretching modes at ~2850 cm^-1 for isolated clathrin-coated vesicles, uncoated vesicles, and synaptic membranes at 21, 38, and 50°C indicated that clathrin significantly increases the number of gauche chain conformers in the bilayer matrix of the coated vesicle system. The increase in lipid disorder at 21°C, accompanying the observed 0.44-cm^-1 frequency increase for coated vesicles compared to uncoated vesicles, is approximately equivalent to the intrachain disorder incurred in heating liquid crystalline dimyristoylphosphatidylcholine multilayers by ~10°C. The implications of these results on coated vesicle formation are discussed.