Structural basis for Lewis antigen synthesis by the α1,3-fucosyltransferase FUT9

Area of Science:

• Biochemistry
• Glycobiology
• Structural Biology

Background:

• Mammalian glycoproteins have diverse glycans crucial for biological functions.
• Lewis antigens, terminal glycan structures, are synthesized by α1,3/4-fucosyltransferases (CAZy GT10 family).
• Existing structural data is limited to bacterial enzymes, distinct from mammalian counterparts.

Purpose of the Study:

• To determine the crystal structures of human FUT9, an α1,3-fucosyltransferase.
• To elucidate substrate specificity determinants and catalytic mechanisms of mammalian GT10 fucosyltransferases.
• To compare mammalian GT10 enzymes with other glycosyltransferases for evolutionary insights.

Main Methods:

• X-ray crystallography of human FUT9 in complex with GDP, acceptor glycans, and a Michaelis complex.
• Kinetic analyses of active site mutants.
• Comparative structural analysis with other GT10 and GT-B fold enzymes.

Main Results:

• Crystal structures of human FUT9 revealed substrate specificity determinants.
• A catalytic model was predicted, supported by kinetic data from mutant analyses.
• Comparisons suggest modular evolution of donor/acceptor binding sites in mammalian GT10 enzymes.

Conclusions:

• The study provides the first structural insights into mammalian α1,3-fucosyltransferases like human FUT9.
• Structural and kinetic data elucidate the mechanism of Lewis antigen synthesis.
• Findings support a model of modular evolution for glycosyltransferases involved in Lewis antigen synthesis.