Visualization of P-selectin glycoprotein ligand-1 as a highly extended molecule and mapping of protein epitopes for monoclonal antibodies - PubMed (original) (raw)

. 1996 Mar 15;271(11):6342-8.

doi: 10.1074/jbc.271.11.6342.

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Visualization of P-selectin glycoprotein ligand-1 as a highly extended molecule and mapping of protein epitopes for monoclonal antibodies

F Li et al. J Biol Chem. 1996.

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Abstract

P-selectin glycoprotein ligand-1 (PSGL-1), a sialomucin on human leukocytes, mediates rolling of leukocytes on P-selectin expressed by activated platelets or endothelial cells under shear forces. PSGL-1 requires both tyrosine sulfate and O-linked glycans to bind P-selectin. Electron microscopy of rotary-shadowed PSGL-1 purified from human neutrophils indicated that it is a highly extended molecule with an extracellular domain that is -50 nm long. Both individual PSGL-1 molecules and rosettes composed of several molecules presumably attached at their transmembrane segments were observed. The extracellular domain of PSGL-1 has 318 residues, including a signal peptide from residues 1-18 and a propeptide from residues 19-41. Using bacterially expressed fusion proteins and synthetic peptides derived from the extracellular domain, we mapped the epitopes for two IgG anti-PSGL-1 monoclonal antibodies, PL1 and PL2. PL2 bound to a region within residues 188-235 that is located in a series of decameric consensus repeats. PL1, which blocks binding of PSGL-1 to P-selectin, recognized an epitope spanning residues 49-62. This sequence overlaps the tyrosine sulfation sites at residues 46, 48, and 51 that have been implicated in binding of PSGL-1 to P-selectin. Our results demonstrate that PSGL-1 is a long, extended molecule and suggest that the P-selectin binding site is located near the N terminus, well above the membrane. This location may facilitate interactions of PSGL-1 with P-selectin under shear stress.

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