Molecular dynamics reveals insight into how N226P and H227Y mutations affect maltose binding in the active site of α-glucosidase II from European honeybee, Apis mellifera

European honeybee, Apis mellifera, produces alpha-glucosidase (HBGase) that catalyzes the cleavage of an alpha-glycosidic bond of the non-reducing end of polysaccharides and has potential applications for malt hydrolysis in brewing industry. Characterized by their substrate specificities, HBGases have three isoforms including HBGase II, which prefers maltose to sucrose as a substrate. Previous study found that the catalytic efficiency of maltose hydrolysis of N226P mutant of HBGase II was higher than that of the wild type (WT), and the catalytic efficiency of maltose hydrolysis of WT was higher than those of H227Y and N226P-H227Y mutants. We hypothesized that N226P mutation probably caused maltose to bind with better affinity and position/orientation for hydrolysis than WT, while H227Y and N226P-H227Y mutations caused maltose to bind with worse affinity and position/orientation for hydrolysis than WT. Using this hypothesis, we performed molecular dynamics on the catalytically competent binding conformations of maltose/WT, maltose/N226P, maltose/H227Y, and maltose/N226P-H227Y complexes to elucidate effects of N226P and H227Y mutations on maltose binding in HBGase II active site. Our results reasonably support this hypothesis because the N226P mutant had better binding affinity, higher number of important binding residues, strong and medium hydrogen bonds as well as shorter distance between atoms necessary for hydrolysis than WT, while the H227Y and N226P-H227Y mutants had worse binding affinities, lower number of important binding residues and strong hydrogen bonds as well as longer distances between atoms necessary for hydrolysis than WT. Moreover, results of binding free energy and hydrogen bond interaction of residue 227 support the role of H227 as a maltose preference residue, as proposed by previous studies. Our study provides important and novel insight into how N226P and H227Y mutations affect maltose binding in HBGase II active site. This knowledge could potentially be used to engineer HBGase II to improve its efficiency.