Expression cloning of a novel alpha 1,3-fucosyltransferase that is involved in biosynthesis of the sialyl Lewis x carbohydrate determinants in leukocytes.

The sialyl Lewis x (NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)Glc-NAc) determinants serve as ligands in the selectin-mediated adhesion of leukocytes to activated endothelium or platelets. In our efforts to identify glycosyltransferases involved in the biosynthesis of those ligands, we achieved expression cloning of a novel human alpha 1,3-fucosyltransferase termed Fuc-TVII from a THP-1 cDNA library by enrichment of the Namalwa cells highly expressing that determinant with a fluorescence-activated cell sorter. Expression of the COOH-terminal catalytic domain of Fuc-TVII showed an alpha 1,3-fucosyltransferase activity for a type II oligosaccharide with a terminal alpha 2,3-linked sialic acid among various acceptors, consistent with that in vivo acceptor specificity. Alignment of the primary sequences of five alpha 1,3-fucosyltransferases and assignment of the chromosomal location of Fuc-TVII gene, together with that acceptor specificity, indicate that Fuc-TVII consists of a unique class of the alpha 1,3-fucosyltransferase family. Determination of the expression levels of these alpha 1,3-fucosyltransferases in various cells revealed that both Fuc-TVII and a myeloid fucosyltransferase Fuc-TIV were significantly expressed in myeloid lineage cells. Fuc-TVII-transfected Namalwa cells exhibited significant binding to E-selectin in contrast to little binding of the Fuc-TIV-transfected cells. These results suggest that Fuc-TVII may participate in the biosynthesis of the selectin ligands.