CHARACTERIZATION OF THE HEPARIN-BINDING PROPERTIES OF ANNEXIN-II TETRAMER

In this report, we have characterized the interaction of heparin with the Ca2+- and phospholipid-binding protein annexin II tetramer (AIIt), Analysis of the circular dichroism spectra demonstrated that the Ca2-dependent binding of AIIt to heparin caused a large decrease in the a -helical content of AIIt from similar to 44 to 31%, a small decrease i n the P-sheet content from similar to 27 to 24%, and an increase in th e unordered structure from 20 to 29%, The binding of heparin also decr eased the Ca2+ concentration required for a half-maximal conformationa l change in AIIt from 360 to 84 mu M. AIIt bound to heparin with an ap parent K-d of 32 +/- 6 nM (mean +/- S.D., n = 3) and a stoichiometry o f 11 +/- 0.9 mol of AIIt/mol of heparin (mean +/- S.D., n = 3), The bi nding of heparin to AIIt was specific as other sulfated polysaccharide s did not elicit a conformational change in AIIt, A region of the p36 subunit of AIIt (Phe(306)-Ser(313)) was found to contain a Cardin-Wein traub consensus sequence for glycosaminoglycan recognition, A peptide to this region underwent a conformational change upon heparin binding, Other annexins contained the Cardin-Weintraub consensus sequence, but did not undergo a substantial conformational change upon heparin bind ing.