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Publication Abstract from PubMed

The domestic silkworm Bombyx mori expresses two sucrose-hydrolyzing enzymes, BmSUH and BmSUC1, belonging to glycoside hydrolase family 13 subfamily 17 (GH13_17) and GH32, respectively. BmSUH has little activity on malto-oligosaccharides, whereas other insect GH13_17 alpha-glucosidases are active on sucrose and maltooligosaccharides. Little is currently known about the structural mechanisms and substrate specificity of GH13_17 enzymes. In this study, we examined the crystal structures of BmSUH without ligands; in complexes with substrates, products, and inhibitors; and complexed with its covalent intermediate at 1.60-1.85 A resolutions. These structures revealed that the conformations of amino acid residues around subsite -1 are notably different at each step of the hydrolytic reaction. Such changes have not been previously reported among GH13 enzymes, including exo- and endo-acting hydrolases, such as alpha-glucosidases and alpha-amylases. Amino acid residues at subsite +1 are not conserved in BmSUH and other GH13_17 alpha-glucosidases, but subsite -1 residues are absolutely conserved. Substitutions in three subsite +1 residues, Gln191, Tyr251, and Glu440, decreased sucrose hydrolysis and increased maltase activity of BmSUH, indicating that these residues are key for determining its substrate specificity. These results provide detailed insights into structure-function relationships in GH13 enzymes and into the molecular evolution of insect GH13_17 alpha-glucosidases.

Structure-function analysis of silkworm sucrose hydrolase uncovers the mechanism of substrate specificity in GH13 subfamily 17 exo-alpha-glucosidases.,Miyazaki T, Park EY J Biol Chem. 2020 May 7. pii: RA120.013595. doi: 10.1074/jbc.RA120.013595. PMID:32381508^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.