Hijacking a biosynthetic pathway yields a glycosyltransferase inhibitor within cells

Glycosyltransferases (GTs) are ubiquitous enzymes that catalyze the assembly of glycoconjugates found throughout all kingdoms of nature. A longstanding problem is the rational design of probes that can be used to manipulate GT activity in cells and tissues. Here we describe the rational design and synthesis of a nucleotide sugar analogue that inhibits, with high potency both in vitro and in cells, the human GT responsible for the reversible post-translational modification of nucleocytoplasmic proteins with O-linked N-acetylglucosamine residues (O-GlcNAc). We show the enzymes of the hexosamine biosynthetic pathway can transform, both in vitro and in cells, a synthetic carbohydrate precursor into the nucleotide sugar analogue. Treatment of cells with the precursor decreases O-GlcNAc in a targeted manner with a single digit micromolar EC50. This approach to inhibition of GTs should be applicable to other members of this increasingly interesting superfamily of enzymes and enable their manipulation in a biological setting.