Enzymes active on glycosidic bonds are defined according to the stereochemistry
of both substrates and products of the reactions they catalyse. The CAZy classification further
assigns these enzymes into sequence-based families sharing a common stereochemistry for
substrates (either α- or β-) and products, i.e. inverting or retaining mechanism. Here we describe
the N-acetylgalactosaminidases AmGH109A and AmGH109B from the human gut symbiont
Akkermansia muciniphila. Notably, AmGH109A displays α-retaining and β-inverting
N-acetylgalactosaminidase activities with comparable efficiencies on natural disaccharides. This
dual specificity could provide an advantage in targeting a broader range of host-derived glycans.
We rationalise this discovery through bioinformatics, structural, mutational, and computational
studies, unveiling a histidine residing in a conserved GGHGG motif as the elusive catalytic acidbase of the GH109 family.
- Glycoside hydrolase
- Human gut microbiota
- Inverting mechanism
- MD simulations