Facile Formation of β-thioGlcNAc Linkages to Thiol-Containing Sugars, Peptides, and Proteins using a Mutant GH20 Hexosaminidase.

Thioglycosides are hydrolase-resistant mimics of O-linked glycosides that can serve as valuable probes for studying the role of glycosides in biological processes. The development of an efficient, enzyme-mediated synthesis of thioglycosides, including S-GlcNAcylated proteins, is reported, using a thioglycoligase derived from a GH20 hexosaminidase from Streptomyces plicatus in which the catalytic acid/base glutamate has been mutated to an alanine (SpHex E314A). This robust, easily-prepared, engineered enzyme uses GlcNAc and GalNAc donors and couples them to a remarkably diverse set of thiol acceptors. Thioglycoligation using 3-, 4-, and 6-thiosugar acceptors from a variety of sugar families produces S-linked disaccharides in nearly quantitative yields. The set of possible thiol acceptors also includes cysteine-containing peptides and proteins, rendering this mutant enzyme a promising catalyst for the production of thio analogues of biologically important GlcNAcylated peptides and proteins.