Fucosyltransferase Family

2) Gaip linkage, but have different acceptor specificities. Whereas the H enzyme highly prefers type-2 chain acceptors and efficiently acts on Gaip-phenyl, the secre-tor enzyme has a preference for type-1 chain-based acceptors and for Gal(pi- 

3) GalNAc [131-133]. The latter enzyme also has much lower affinity for the donor substrate GDP-Fuc than the H enzyme [131, 133]. In rabbit three o2-FucTs occur one resembles the human H enzyme in molecular and enzymatic properties, the others are molecularly similar to, and have the enzymatic characteristics of, the secretor enzyme [134]. 

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Another specific modification of polylactosaminoglycan chains is the introduction of a3-Fuc residues to non-terminal GlcNAcs along the chain to yield a (sialyl-) oligomeric-Lewis structure. In leukocytes the formation of this structure, which is a ligand for E- and P-selectin, is catalyzed by two different a3-FucTs, the myeloid FucT (FucT IV) and the leukocyte FucT (FucT VII) [92, 93] (Figure 10) (see also Section 23.20, o314-Fucosyltransferase Family below). 

Within the a3/4-fucosyltransferase family six different members have been identified. They are numbered in the order they were cloned FucT III-VII and IX. Human FucT III (Lewis enzyme), V and VI (hver/plasma enzyme) are highly related enzymes with >90% identity at the amino acid level in their catalytic domain their genes are all located on human chromosome 19 [135]. By contrast, FucT IV (myeloid enzyme, chromosome 11) and FucT VII (leukocyte enzyme, chromosome 9) have a more distal relationship to each other and to the other members of this family [135, 136]. Recently a novel member, FucT IX, which has highest homology to FucT rv, was cloned from a mouse library [137]. Recently the human ortholog of FucT IX was described [138]. 

FucT, Gal(al-3)Gal (al-2)FucT and GaI(al-3)[Fuc(al-2)]Gal (al-2)FucT can be postulated. As a further attempt to correlate the structure of the enzyme with the specific activity, such a model should be investigated by molecular cloning of this family of fucosyltransferases. 

B. W. Weston, P. L. Smith, R. J. Kelly, J. B. Lowe, Molecular cloning of a fourth member of a human alpha (l,3)fucosyltransferase gene family. Multiple homologous sequences that determine expression of the Lewis x, sialyl Lewis x, and difucosyl sialyl Lewis x epitopes [ published erratum appears in J Biol Chem 1993 Aug 25 268(24) 18398], J Biol Chem, (1992), 267, 24575-84. 

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