CD31 (PECAM-1) exists as a dimer and is heavily N-glycosylated

CD31 (PECAM-1) is a highly abundant cell surface glycoprotein expressed on hemopoietic and endothelial cells where it functions as a hemophilic adhesi on and signaling receptor. Since dimerization and appropriate glycosylation are important features in the regulation of cell surface interactions and signal transduction, we studied the pattern of glycosylation as well as the ability of CD31 to undergo dimerization, both in solution and when express ed on cell membranes. CD31 is heavily glycosylated, with an approximate car bohydrate content of 21%. Nineteen neutral and thirteen sialylated glycans were identified. Ultracentrifugation analysis showed that soluble recombina nt CD31 exists in equilibrium between a monomer and a dimer with an approxi mate dissociation constant of 12.5 mu M. Chemical cross-linking studies of both soluble and membrane-expressed CD31 confirmed that CD31 exists as a di mer, These studies suggest that, like E-cadherin, PECAM-dimerization is lik ely to play a role in CD31 adhesion and signaling. (C) 1999 Academic Press.