The α(1,3)-fucosyltransferase Fuc-TIV, but not Fuc-TVII, generates sialyl Lewis X-like epitopes preferentially on glycolipids

Abstract

Fuc-TIV and Fuc-TVII are the two α(1,3)-fucosyltransferases in myeloid cells responsible for the biosynthesis of sialyl Lewis X (sLex), the minimal ligand structure for the selectins. We have compared the ability of Fuc-TIV and Fuc-TVII to generate sLex-like epitopes in transfected Chinese hamster ovary (CHO)-Pro-5 cells expressing the P-selectin glycoprotein ligand-1 and the core-2 branching enzyme C2GnT. We found that mouse Fuc-TIV and Fuc-TVII can generate similar levels of cell surface sLex. Surprisingly however, Fuc-TIV-generated sLex was resistant to proteinase K and trypsin treatment and could be removed from cells by delipidation with chloroform/methanol, whereas 80-90% of Fuc-TVII-generated sLex was protease-sensitive, and most of it resistant to delipidation. Despite similar levels of sLex on the cell surface, Fuc-TVII transfectants adhered to immobilized E-selectin-IgG under static and flow conditions better than Fuc-TIV transfectants. Binding was mainly protease sensitive, indicating that glycoproteins were more efficient ligands than glycolipids. In summary, we conclude that the two fucosyltransferases differ in their in vivo specificity for acceptor substrates with Fuc-TVII generating sLex preferentially on glycoproteins, whereas most of the Fuc-TIV-generated sLex is found on glycolipids. Interestingly, the non-catalytic portion of Fuc-TIV in a Fuc-TIV/VII chimeric enzyme mediated the specificity for glycolipid substrates.