Fig. 1.

Catalytic mechanisms in GTs. (A) GTs catalyze the transfer of sugars with either “inversion” or “retention” of the anomeric configuration with respect to the sugar donor substrates. (B) Inverting GTs utilize a direct-displacement S_N2-like reaction mechanism involving a single oxocarbenium ion-like transition state. (C) Current mechanisms for enzymatic glycosyl transfer with retention of configuration proposed in the literature: The front-face mechanism and the double-displacement mechanism (Rojas-Cervellera et al. 2013).