DFT study of sucrose hydrolysis by a GH32 cell-wall invertase, a key enzyme in carbohydrate metabolism

The Arabidopsis thaliana cell-wall invertase 1 (AtCWIN1), a member of the family 32 glycoside hydrolase (GH32), hydrolyzes sucrose into fructose and glucose via a retaining mechanism. AtCWIN1 plays a key role in sucrose metabolism in plant. Here, the reaction mechanism of the GH32 AtCWIN1 enzyme has been investigated using quantum chemical approach. Two alternative orientations of an acid/base catalyst (Glu203) with regard to the location of the pKa modulators (Arg148 and Tyr279) are investigated to understand the involvement of these pKa residues in the reaction. The calculations suggested that the orientation involving a hydrogen bond network (Arg148•••Glu203•••Tyr279) is energetically more favourable than the other (Arg148•••Glu203), with a barrier of 17.5 kcal mol−1, which is consistent with the experimental value (15.3 kcal/mol). This Arg148•••Glu203•••Tyr279 interaction provides a strong H-bond network that stabilises the reaction effectively. Overall, this study demonstrates that the enzymatic activity in AtCWIN1 depends on a hydrogen bond network created by the residues Arg148, Glu203, and Tyr279.