Incorporation of blood-clotting proteins into phospholipid Langmuir monolayers: A fluorescence microscopy study

Phospholipid monolayers adsorbed at an air-water interface are model cell m embranes and have been used in this work to study interactions with blood-c lotting proteins. Factor I(non-membrane binding) was used as a control prot ein, and its association with L-alpha -dipalmitoylphosphatidylcholine Langm uir monolayers was compared to factor VII, a membrane-binding protein. Fluo rescence micrographs indicated that factor I penetration of the lipid monol ayers in the phase transition region occurred extensively, causing condensa tion of the lipid film, The association of factor I with phospholipid monol ayers was deemed nonspecific. Factor VII was shown to associate with the pe riphery of lipid domains in the absence of calcium ions, causing flattening of domain edges. In the presence of calcium, factor VII induced expansion of the lipid monolayer. This effect is a specific interaction attributed to exposure of hydrophobic residues upon calcium binding, followed by protein association with lipid hydrocarbon chains. (C) 2001 Academic Press.