title: Structural insight into substrate specificity of human intestinal maltase-glucoamylase.
abstract: Human maltase-glucoamylase (MGAM) hydrolyzes linear alpha-1,4-linked oligosaccharide substrates, playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 diabetes and obesity. The amino- and carboxyl-terminal portions of MGAM (MGAM-N and MGAM-C) carry out the same catalytic reaction but have different substrate specificities. In this study, we report crystal structures of MGAM-C alone at a resolution of 3.1 Å, and in complex with its inhibitor acarbose at a resolution of 2.9 Å. Structural studies, combined with biochemical analysis, revealed that a segment of 21 amino acids in the active site of MGAM-C forms additional sugar subsites (+ 2 and + 3 subsites), accounting for the preference for longer substrates of MAGM-C compared with that of MGAM-N. Moreover, we discovered that a single mutation of Trp1251 to tyrosine in MGAM-C imparts a novel catalytic ability to digest branched alpha-1,6-linked oligosaccharides. These results provide important information for understanding the substrate specificity of alpha-glucosidases during the process of terminal starch digestion, and for designing more efficient drugs to control type 2 diabetes or obesity.
authors: State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.
authors: Limei
authors: L
authors: Ren
authors: Xiaohong
authors: X
authors: Qin
authors: Xiaofang
authors: X
authors: Cao
authors: Lele
authors: L
authors: Wang
authors: Fang
authors: F
authors: Bai
authors: Gang
authors: G
authors: Bai
authors: Yuequan
authors: Y
authors: Shen
mesh_terms: D020909:Acarbose / Q000737:chemistry; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D065089:Glycoside Hydrolase Inhibitors; D006801:Humans; D006860:Hydrogen Bonding; D007422:Intestines / Q000201:enzymology*; D007700:Kinetics; D008320:Maltose / Q000737:chemistry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009844:Oligosaccharides / Q000737:chemistry; D010843:Pichia; D011485:Protein Binding; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics; D013379:Substrate Specificity; D013499:Surface Properties; D000520:alpha-Glucosidases / Q000737:chemistry* / Q000235:genetics
chemical_list: D065089:Glycoside Hydrolase Inhibitors; D009844:Oligosaccharides; D011994:Recombinant Proteins; D008320:Maltose; D000520:alpha-Glucosidases; D020909:Acarbose