Kinetics and thermodynamics of annexin A1 binding to solid-supported membranes: A QCM study

By means of the quartz crystal microbalance (QCM) technique, the interaction of annexin Al with lipid membranes was quantified using solid-supported bilayers immobilized on gold electrodes deposited on 5 MHz quartz plates. Solid-supported lipid bilayers were composed of a first octanethiol monolayer chemisorbed on gold and a physisorbed phospholipid monolayer obtained from vesicle fusion. This experimental setup enabled us to determine for the first time rate constants and affinity constants of annexin Al binding to phosphatidylserine-containing layers as a function of the calcium ion concentration in solution and the cholesterol content within the outer leaflet of the solid-supported bilayer. The results reveal that a decrease in Ca2+ concentration from 1 mM to 100 muM significantly increases the rate of annexin A] binding to the membrane independent of the cholesterol content. However, the presence of cholesterol in the membrane altered the affinity constants considerably. While the association constant decreases with decreasing Ca2+ concentration in the case of 1-paimitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS) membranes lacking cholesterol, it remains high in the presence of cholesterol.