Structure of phosphatidyl serine (PS) involved in interbilayer salt bridging and hydrogen bonding

For understanding the experimental results indicating salt bridging and hydrogen bonding between opposite polar surfaces in planar multibilayer structures of phosphatidyl serine (PS), (1) we carried out molecular modeling of the interacting surface layers. The interacting structures in the planar multibilayers are stabilized by salt bridge arrays of the phosphates with their counterions and by hydrogen bonds of ammonia from one polar surface with carbonyls in the opposite one. In multishell liposomes, where the distances between phosphates on the facing each other surfaces are not equal and they are bound to get out of register, the interbilayer interaction cannot extend over a large enough area to form stable structures, except if the salt bridges are strong enough to break down the curved surfaces and form planar multibilayers.