VOLTAGE-DEPENDENT BINDING OF ANNEXIN-V, ANNEXIN-VI AND ANNEXIN-VII CORE TO ACIDIC PHOSPHOLIPID-MEMBRANES

Annexin V, VI and VII-core (Delta 1-107) are members of the annexin pr otein family and bind to acidic phospholipid membranes in a calcium de pendent manner. They also show ion channel activity under certain cond itions. As annexins bind peripherally to lipid membranes, ion channel formation must consist of at least two steps: An adsorption reaction r egulating the binding of annexin to the membrane surface and the openi ng and closing of the active species controlling the channel activity. By using the baseline current through the patch clamp seal as a probe for unoccupied binding sites at the membrane, we show that the adsorp tion of annexins to membranes is not only calcium dependent but also s trongly voltage dependent. Whereas the free transfer energies at low c alcium concentrations are similar for all three annexins, the binding of annexin V becomes much tighter with higher calcium levels, compared to annexin VI and VII-core. This correlates with the finding that ann exin VI and VII-core display channel activity much more often than ann exin V if one assumes that a high coverage of the membrane surface wit h annexins stabilizes the bilayer. At higher protein concentrations we aker binding is observed in agreement with the previously reported ant i-cooperativity of membrane binding. (C) 1997 Elsevier Science B.V.