Structural basis for substrate specificity and catalysis of α1,6-fucosyltransferase

Core-fucosylation is an essential biological modification by which a fucose is transferred from GDP-beta-L-fucose to the innermost N-acetylglucosamine residue of N-linked glycans. A single human enzyme alpha 1,6-fucosyltransferase (FUT8) is the only enzyme responsible for this modification via the addition of an alpha-1,6-linked fucose to N-glycans. To date, the details of substrate recognition and catalysis by FUT8 remain unknown. Here, we report the crystal structure of FUT8 complexed with GDP and a biantennary complex N-glycan (G0), which provides insight into both substrate recognition and catalysis. FUT8 follows an S(N)2 mechanism and deploys a series of loops and an alpha-helix which all contribute in forming the binding site. An exosite, formed by one of these loops and an SH3 domain, is responsible for the recognition of branched sugars, making contacts specifically to the alpha 1,3 arm GlcNAc, a feature required for catalysis. This information serves as a framework for inhibitor design, and helps to assess its potential as a therapeutic target. Core-fucosylation of the N-glycan core is an essential biological modification and the alpha 1,6- fucosyltransferase FUT8 is the only enzyme in humans that catalyses this modification through the addition of an alpha-1,6-linked fucose to N-glycans. Here the authors provide insights into FUT8 substrate recognition by determining the 1.95 angstrom crystal structure of human FUT8 complexed with GDP and a biantennary complex N-glycan.