A SULFATED PEPTIDE SEGMENT AT THE AMINO-TERMINUS OF PSGL-1 IS CRITICAL FOR P-SELECTIN BINDING

P-selectin glycoprotein ligand 1 (PSGL-1) is a mucin-like glycoprotein expressed on the surface of myeloid cells and serves as the high affi nity counterreceptor for P-selectin. The PSGL-1-P-selectin interaction is calcium dependent and requires presentation of sialyl-Lewis(x) (sL e(x))-type structures on the O-linked glycans of PSGL-1. We report her e the identification of a noncarbohydrate component of the binding det erminant that is critical for high affinity binding to P-selectin. Loc ated within the first 19 amino acids, this anionic polypeptide segment contains at least one sulfated tyrosine residue, We propose that this sulfotyrosine-containing segment of PSGL-1, in conjunction with sLe(x ) presented on O-linked glycans, constitutes the high affinity P-selec tin-binding site.