Visualization of Annexin I Binding to Calcium-Induced Phosphatidylserine Domains

A monomolecular protein adsorption was observed for the binding of annexin I to phosphatidylserine-enriched lipid domains. The interactions of this membrane-associated protein (red in the picture; green=N terminus, •=Ca2+-binding site) with phospholipid bilayers immobilized on mica were visualized by scanning force microscopy. Domain formation in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/-phosphoserine layers was induced by Ca2+ ions rather than by the protein itself, as demonstrated by time-of-flight secondary-ion mass spectrometric analysis and lateral force microscopy.