Unlocking the hydrolytic mechanism of GH92 α-1,2-mannosidases: computation inspires using C-glycosides as Michaelis complex mimics

The conformational changes in a sugar moiety along the hydrolytic pathway are key to understand the mechanism of glycoside hydrolases (GHs) and to design new inhibitors. The two predominant itineraries for mannosidases go via OS2  B2,5  1S5 and 3S  3H4  1C4. For the CAZy family 92, the conformational itinerary was unknown. Published complexes of Bacteroides thetaiotaomicron GH92 catalyst with a S-glycoside and mannoimidazole indicate a 4C1  4H5/1S5  1S5 mechanism. However, as observed with the GH125 family, S-glycosides may not act always as good mimics of GH’s natural substrate. Here we present a cooperative study between computations and experiments where our results predict the E5  B2,5/1S5  1S5 pathway for GH92 enzymes. Furthermore, we demonstrate the Michaelis complex mimicry of a new kind of C-disaccharides, whose biochemical applicability was still a chimera.