CONFORMATIONAL ADAPTATION OF ANNEXIN-V UPON BINDING TO LIPOSOMES - A TIME-RESOLVED FLUORESCENCE STUDY

The fluorescence intensity decay of the single tryptophan residue, Trp -187, of free annexin V is described by the sum of three lifetime comp onents (5.4, 1.3, and 0.4 ns), which may be correlated to three ground -state classes of Trp conformers. The two major classes (44 and 48%) a re embedded in the protein matrix. When annexin V binds to calcium and liposomes made of dioleoylphosphatidylcholine and dioleoylphosphatidy lserine, similar results are obtained whatever the (10-200) lipid rati o. The Trp fluorescence decay is fitted with only two components (6.9- 7.2 and 2.0-2.2 ns). Decay-associated spectra reveal that the longest lifetime of bound annexin V can be related to Trp residues (60%) locat ed in a partially polar environment, which could correspond to the pro tein-membrane interface. The shortest lifetime is attributed to Trp re sidues (40%) which reside in a hydrophobic surrounding: these Trp resi dues would penetrate into the phospholipid membrane and contribute to the stabilization of the 2D-array of annexin V molecules. (C) 1997 Aca demic Press.