Glycobiology, 2002, Vol. 12, No. 10 599-606
© 2002 Oxford University Press
A highly conserved His-His motif present in 
1
3/4fucosyltransferases is required for optimal activity and functions in acceptor binding
Northwest Hospital, Molecular Medicine, Department of Cell Surface Biochemistry, 21720 23rd Drive SE, Suite 101, Bothell, WA 98021, USA
1
3/4Fucosyltransferases (FucTs) from several species contain a highly conserved His-His motif adjacent to an enzyme region correlating with the ability to catalyze fucose transfer to type 1 chain acceptors. Site-directed mutagenesis has been employed to analyze structure–function relationships of this His-His motif in human FucT-IV. The results indicate that most changes of His113 and His114 and nearby residues of FucT-IV reduced the specific activity of the enzymes. Analysis of acceptor properties demonstrated close similarity of most mutants with wild-type FucT-IV, whereas an apparent preference for the H-type II acceptor was observed for the His114 mutants. Kinetic studies demonstrated that mutants of His114 had a substantially increased Km for acceptor compared to other enzymes tested. The dramatic increase in acceptor Km for the His114 mutants, particularly for the nonfucosylated acceptor, suggests that this His-His motif is involved in acceptor binding and perhaps interacts with GlcNAc residues of type 2 acceptors. The presence of fucose in acceptor substrates may promote more efficient substrate binding and presumably partially overcomes the weaker interaction with GlcNAc caused by the mutation.
1 To whom correspondence should be addressed; E-mail: eholmes@nwbio.com
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