Identification of the catalytic acid-base residue of arthrobacter endo-β-N-acetylglucosaminidase by chemical rescue of an inactive mutant

Arthrobacter endo-β-N-acetylglucosaminidase (Endo-A), a member of glycoside hydrolase (GH) family 85, catalyses the hydrolysis and transglycosylation of asparagine-linked oligosaccharides of glycoproteins with retention of anomeric configuration. Glu-173 of Endo-A is a catalytically essential amino acid residue, and the corresponding residue is conserved in all GH family 85 members. The catalytic activity of Endo-A E173A mutant was rescued by the addition of sodium azide or sodium formate. Furthermore, the produced β-glycosyl azide (Man ₅GlcNAc-β-N ₃) retained the anomeric configuration, indicating that Glu-173 is the catalytic acid-base residue of Endo-A. This is the first identification of the catalytic residue for GH family 85 endo-β-N-acetylglucosaminidases.