Abstract
The alpha1,3/4 fucosyltransferase (FucT) enzyme from Helicobacter pylori catalyzes fucose transfer from donor GDP-beta-l-fucose to the GlcNAc group of two series of acceptor substrates in H. pylori lipopolysaccharide: betaGal1,3betaGlcNAc (Type I) or betaGal1,4betaGlcNAc (Type II). Fucose is added either in alpha1,3 linkage of Type II acceptor to produce Lewis X or in alpha1,4 linkage of Type I acceptor to produce Lewis A, respectively. H. pylori FucTs from different strains have distinct Type I or Type II substrate specificities. FucT in H. pylori strain NCTC11639 has an exclusive alpha1,3 activity because it recognizes only Type II substrates, whereas FucT in H. pylori strain UA948 can utilize both Type II and Type I acceptors; thus it has both alpha1,3 and alpha1,4 activity, respectively. To identify elements conferring substrate specificity, 12 chimeric FucTs were constructed by domain swapping between 11639FucT and UA948FucT and characterized for their ability to transfer fucose to Type I and Type II acceptors. Our results indicate that the C-terminal region of H. pylori FucTs controls Type I and Type II acceptor specificity. In particular, the highly divergent C-terminal portion, seven amino acids DNPFIFC at positions 347-353 in 11639FucT, and the corresponding 10 amino acids CNDAHYSALH at positions 345-354 in UA948FucT, controls the Type I and Type II acceptor recognition. This is the opposite of mammalian FucTs where acceptor preference is determined primarily by the N-terminal residues in the hypervariable stem domain.
Highlights
The lipopolysaccharide (LPS) of H. pylori contains fucosylated oligosaccharides, predominantly the Type II blood group antigens Lewis X and Lewis Y (1)
The C-terminal catalytic domain of mammalian FucTs displays a low level of amino acid sequence identity (40%) with the internal catalytic domain of H. pylori FucTs (8)
In comparison with mammalian FucTs, H. pylori FucTs do not have N-terminal tails or transmembrane domains, instead, they contain heptad repeats at their C-terminus, which are absent in human FucTs (8,11)
Summary
The lipopolysaccharide (LPS) of H. pylori contains fucosylated oligosaccharides, predominantly the Type II blood group antigens Lewis X and Lewis Y (1). In H. pylori genomes (4,5), there exist two homologous α1,3/4 FucT genes, futA and futB and one gene futC for α1,2 FucT (6). These three fut genes do not always encode functional proteins. The C-terminal catalytic domain of mammalian FucTs displays a low level of amino acid sequence identity (40%) with the internal catalytic domain of H. pylori FucTs (8). This domain contains two highly conserved regions, referred to as the α1,3/4 FucT motifs (10,11). In comparison with mammalian FucTs, H. pylori FucTs do not have N-terminal tails or transmembrane domains, instead, they contain heptad repeats at their C-terminus, which are absent in human FucTs (8,11)
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