Interaction between lipopolysaccharide (LPS), LPS-binding protein (LBP), and planar membranes

The mechanism of interaction of the lipopolysaccharide (LPS)-binding protei n, LBP, with differently composed symmetric and asymmetric planar lipid bil ayers was investigated in electrical measurements (membrane current, potent ial, capacitance). From a change of the inner membrane potential difference , binding of LBP to membranes was deduced. After addition of LBP to one sid e of the membrane, binding of anti-LBP antibodies and LPS to LBP on both si des of the bilayer was observed. Effects resulting from an interaction of a nti-LBP antiserum with membrane-bound LBP depend on the side of addition of the antiserum, indicating a directed intercalation of LBP into the membran e. Addition of LPS to the same side as LBP may induce a change of the confo rmation of LBP or its orientation in the membrane. Based on these observati ons, we propose that LBP intercalates in a directed orientation into negati vely-charged membranes and assumes a transmembrane configuration. Moreover, pre-incubated complexes of LPS and LBP do not interact with membranes. The se experiments show that reconstituted planar membranes are a suitable tool for investigations of the interaction of non pore-forming proteins that ar e involved in signal transduction.