DIVALENT CATION-DEPENDENT STRUCTURE IN THE PLATELET MEMBRANE GLYCOPROTEIN IA-IIA (VLA-2) COMPLEX

Recent studies have shown that the platelet membrane glycoprotein Ia-IIa (VLA-2) complex mediates the Mg++-dependent adhesion of platelets to collagen and that this adhesion is inhibited by Ca++ in a simple, linear, noncompetitive manner. These findings suggested that separate binding sites for Mg++ and Ca++ stabilize different divalent cation-dependent structures within the receptor complex. To provide evidence for the existence of such structures purified platelet Ia-IIa complex was subjected to limited proteolytic digestion in the presence of Mg++, Ca++, Mg++ and Ca++, or EDTA and the resulting peptides mapped by SDS-PAGE using both one- and two-dimensional techniques. Unique patterns of tryptic peptides were produced under each of the conditions. The results indicate that Mg++ and Ca++ stabilize different structures within the Ia-IIa (VLA-2) complex and that these structures influence both the collagen binding activity and proteolytic susceptibility of the complex. © 1990.