摘要
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 3.1Å,and in complex with its inhibitor acarbose at a resolution of 2.9Å.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 alphaglucosidases during the process of terminal starch digestion,and for designing more efficient drugs to control type 2 diabetes or obesity.
基金
by the National Basic Research Program of China(973 Program)(Grant Nos.2007CB914301 and 2007CB 914803)
the Natural Science Foundation of China(Grant Nos.30940015,30770428,21002052 and 31170684)
the TBR Program(No.08QTPTJC 28200,08SYSYTC00200 and 10JCYB JC14300).
