Binding of vascular anticoagulant alpha (VAC alpha) to planar phospholipid bilayers.
Vascular anticoagulant alpha (VAC alpha, annexin V) is a member of the family of calcium and phospholipid binding proteins, the annexins. The binding properties of VAC alpha to phospholipid bilayers were studied by ellipsometry. Adsorption was calcium-dependent and completely reversible upon calcium depletion. Half-maximal adsorptions to phospholipid bilayers consisting of 100, 20, 5, and 1% dioleoyl-phosphatidylserine (DOPS) supplemented with dioleoyl-phosphatidylcholine (DOPC) were reached at Ca2+ concentrations of 0.04, 0.22, 1.5, and 8.6 mM. These surfaces all showed the same maximal adsorption of 0.22 +/- 0.01 micrograms of VAC alpha/cm2 (mean +/- S.D.). The adsorption to bilayers containing more than 10% DOPS was independent of VAC alpha concentrations in the range of 0.5-100 nM. Dissociation constants for VAC alpha binding to these surfaces were estimated to be below 2 x 10(-10) M. No adsorption was observed on pure DOPC bilayers at a Ca2+ concentration of 3 mM. The ability to mediate VAC alpha binding to 20% DOPS/80% DOPC bilayers was highly specific for Ca2+. The use of other divalent cations resulted in decreased binding in the order Cd2+ greater than Zn2+ greater than Mn2+ greater than Co2+ greater than Ba2+ greater than Mg2+. Zinc ions had a synergistic effect on Ca2(+)-dependent VAC alpha binding. The Ca2+ concentration needed for half-maximal binding to cardiolipin, dioleoyl-phosphatidylglycerol, DOPS, phosphatidylinositol, phosphatidic acid, dioleoyl-phosphatidylethanolamine, and sphingomyelin increased in that order. Adsorption was independent of the overall surface charge of the phospholipid membrane.
Andree
H A
HA
Institute for Cardiovascular Research, University of Limburg, Maastricht, The Netherlands.
Reutelingsperger
C P
CP
Hauptmann
R
R
Hemker
H C
HC
Hermens
W T
WT
Willems
G M
GM
D000327:Adsorption; D017302:Annexins; D001777:Blood Coagulation; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D004563:Electrochemistry; D007700:Kinetics; D008051:Lipid Bilayers; D010455:Peptides / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D015032:Zinc / Q000494:pharmacology
D017302:Annexins; D002413:Cations, Divalent; D008051:Lipid Bilayers; D010455:Peptides; D010743:Phospholipids; D011994:Recombinant Proteins; D015032:Zinc; D002118:Calcium