I am presently working on MIP and annexins in lipid bilayers. The following is an abstract presented at the Biophysical society meeting in New Orleans.
ANNEXIN INTERACTION WITH PLANAR LIPID BILAYERS. ((Y.V. Sokolov, N. Tranngo, W. Mailliard, H. Haigler, H. Luecke and J. E. Hall)) University of California, Irvine; Irvine, CA 92697-4560.
Annexins are a family of calcium- and phospholipid-binding proteins thought to be involved in a number of membrane processes including fusion and secretion. Recent studies of annexin XII showed that it forms a calcium-dependent homo-hexamer. To study phospholipid binding of annexin XII we used a lipid bilayer containing nonactin as a conductance probe. Annexin XII added to a solution bathing the lipid bilayer decreased the nonactin-induced conductance in a concentration-dependent manner. This dependence was well fit by an adsorption isotherm with an apparent pK of 6.8. Nonactin conductance reduction required phosphatidylserine in the lipid bilayer and was strongly dependent on calcium (but not magnesium) concentration in the range of 0.03 - 1 mM. Two annexin XII mutants which are not able to form hexamers (E105K and the double mutant, E105K/K68A) were much less effective. The conductance reduction of both could be fit by adsorption isotherms with pK of about 5.4. A third mutant (K132E) having a mutation in the central region of the molecule which did not affect hexamer formation had an effect on the nonactin conductance similar to that of wild type annexin XII. The possible mechanisms of annexin-phospholipid interaction are discussed. This work was supported by NIH grant EY5661 to JEH.