Molecular reorganization of lipid bilayers by complement: a possible mechanism for membranolysis.

Abstract

The interaction between the membrane attack complex (MAC) of complement and flat lipid bilayers was investigated. The penetration of the MAC into bilayers and its influence on the order of bilayers was measured using spin-labeled phospholipid derivatives and EPR spectroscopy. The MAC precursor components C5b-6, C7, C8 and C9 did not exert any measurable influence on lipid membranes. Functional C5b-7 interacted strongly with the bilayer surface without deep penetration into the bilayer. Formation of C5b-8 and especially C5b-9 caused a marked change in the anisotropy of spectra from probes located within the hydrocarbon phase. The spectral changes are not caused by changes in probe rotation and in the case of the cholesterol probes, are not due to direct probe-protein interactions. The spectral changes may be the result of reorientation of ordered bilayer lipids effected by strong binding of phospholipids to MAC proteins.