Activity, splice variants, conserved peptide motifs, and phylogeny of two New α1,3-fucosyltransferase families (FUT10 and FUT11)

Abstract

We report the cloning of three splice variants of the FUT10 gene, encoding for active α-L-fucosyltransferase-isoforms of 391, 419, and 479 amino acids, and two splice variants of the FUT11 gene, encoding for two relatedα-L-fucosyltransferases of 476 and 492 amino acids. The FUT10 and FUT11 appeared 830 million years ago, whereas the other α1,3-fucosyltransferases emerged 450 million years ago. FUT10-391 and FUT10-419 were expressed in human embryos, whereas FUT10-479 was cloned from adult brain and was not found in embryos. Recombinant FUT10-419 and FUT10-479 have a type II trans-membrane topology and are retained in the endoplasmic reticulum (ER) by a membrane retention signal at their NH2 termini. The FUT10-479 has, in addition, a COOH-ER membrane retention signal. The FUT10-391 is a soluble protein without a transmembrane domain or ER retention signal that transiently localizes to the Golgi and then is routed to the lysosome. After transfection in COS7 cells, the three FUT10s and at least one FUT11, link α-L-fucose onto conalbumin glycopeptides and biantennary N-glycan acceptors but not onto short lactosaminyl acceptor substrates as do classical monoexonic α1,3-fucosyltransferases. Modifications of the innermost core GlcNAc of the N-glycan, by substitution with ManNAc or with an opened GlcNAc ring or by the addition of an α1,6-fucose, suggest that the FUT10 transfer is performed on the innermost GlcNAc of the core chitobiose. We can exclude α1,3-fucosylation of the two peripheral GlcNAcs linked to the trimannosyl core of the acceptor, because the FUT10 fucosylated biantennary N-glycan product loses both terminal GlcNAc residues after digestion with human placenta α-N-acetylglucosaminidase. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.