title: Binding of glycosulfopeptides to P-selectin requires stereospecific contributions of individual tyrosine sulfate and sugar residues.
abstract: P-selectin glycoprotein ligand-1 (PSGL-1) is a mucin on leukocytes that binds to selectins. P-selectin binds to an N-terminal region of PSGL-1 that requires sulfation of at least one of three clustered tyrosines (TyrSO(3)) and an adjacent core-2-based O-glycan expressing sialyl Lewis x (C2-O-sLe(x)). We synthesized glycosulfopeptides (GSPs) modeled after this region of PSGL-1 to explore the roles of individual TyrSO(3) residues, the placement of C2-O-sLe(x) relative to TyrSO(3), the relative contributions of fucose and sialic acid on C2-O-sLe(x), and the function of the peptide sequence for binding to P-selectin. Binding of GSPs to P-selectin was measured by affinity chromatography and equilibrium gel filtration. 2-GSP-6, which has C2-O-sLe(x) at Thr-57 and TyrSO(3) at residues 46, 48, and 51, bound to P-selectin with high affinity (K(d) approximately 650 nm), whereas an isomeric trisulfated GSP containing C2-O-sLe(x) at Thr-44 bound much less well. Non-sulfated glycopeptide (2-GP-6) containing C2-O-sLe(x) at Thr-57 bound to P-selectin with approximately 40-fold lower affinity (K(d) approximately 25 microm). Proteolysis of 2-GP-6 abolished detectable binding of the residual C2-O-sLe(x)-Thr to P-selectin, demonstrating that the peptide backbone contributes to binding. Monosulfated and disulfated GSPs bound significantly better than non-sulfated 2-GP-6, but sulfation of Tyr-48 enhanced affinity (K(d) approximately 6 microm) more than sulfation of Tyr-46 or Tyr-51. 2-GSP-6 lacking sialic acid bound to P-selectin at approximately 10% that of the level of the parent 2-GSP-6, whereas 2-GSP-6 lacking fucose did not detectably bind; thus, fucose contributes more than sialic acid to binding. Reducing NaCl from 150 to 50 mm markedly enhanced binding of 2-GSP-6 to P-selectin (K(d) approximately 75 nm), demonstrating the charge dependence of the interaction. These results reveal a stereospecific interaction of P-selectin with PSGL-1 that includes distinct contributions of each of the three TyrSO(3) residues, adjacent peptide determinants, and fucose/sialic acid on an optimally positioned core-2 O-glycan.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
authors.forename: A
authors.initials: A
authors.lastname: Leppänen
authors.forename: S P
authors.initials: SP
authors.lastname: White
authors.forename: J
authors.initials: J
authors.lastname: Helin
authors.forename: R P
authors.initials: RP
authors.lastname: McEver
authors.forename: R D
authors.initials: RD
authors.lastname: Cummings
mesh_terms: D000595:Amino Acid Sequence; D050260:Carbohydrate Metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D005643:Fucose / Q000378:metabolism; D006023:Glycoproteins; D007536:Isomerism; D007700:Kinetics; D013058:Mass Spectrometry; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008954:Models, Biological; D008956:Models, Chemical; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D019007:P-Selectin / Q000378:metabolism*; D010455:Peptides; D011402:Pronase / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C121374:GSP-6 glycosulfopeptide; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D019007:P-Selectin; D010455:Peptides; D011994:Recombinant Proteins; D005643:Fucose; C005662:tyrosine O-sulfate; D014443:Tyrosine; D012965:Sodium Chloride; D011402:Pronase; D019158:N-Acetylneuraminic Acid