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Publication Abstract from PubMed

Arthrobacter globiformis T6 isomaltodextranse (AgIMD) is an enzyme that liberates isomaltose from the non-reducing end of a polymer of glucose, dextran. AgIMD is classified as a member of glycoside hydrolase family (GH) 27, which comprises mainly alpha-galactosidases and alpha-N-acetylgalactosaminidases, whereas AgIMD does not show alpha-galactosidase or alpha-N-acetylgalactosaminidase activities. Here we determined the crystal structure of AgIMD. AgIMD consists of three domains: A, C, and D. Domains A and C are identified as a (beta/alpha)8-barrel catalytic domain and an antiparallel beta-structure, respectively, both of which are commonly found in GH27 enzymes. However, domain A of AgIMD has subdomain B, loop-1, and loop-2, all of which are not found in GH27 human alpha-galactosidase. AgIMD in a complex with trisaccharide panose shows that Asp207, a residue in loop-1, is involved in subsite +1. Kinetic parameters of the wild-type and mutant enzymes for a small synthetic saccharide, p-nitrophenyl alpha-isomaltoside, and the polysaccharide, dextran, were compared, showing that Asp207 is important for the catalysis of dextran. Domain D is classified as carbohydrate-binding module (CBM) 35, and an isomaltose molecule is seen in this domain in the AgIMD-isomaltose complex. Domain D is highly homologous to CBM35 domains found in GH31 and GH66 enzymes. The results here indicate that some features found in GH13, 31, and 66 enzymes, such as subdomain B, residues at subsite +1, and the CBM35 domain, are also observed in the GH27 enzyme, AgIMD, and thus provide insights into the evolutionary relationships among GH13, 27, 31, 36, and 66 enzymes.

Crystal structure and mutational analysis of isomaltodextranase, a member of glycoside hydrolase family 27.,Okazawa Y, Miyazaki T, Yokoi G, Ishizaki Y, Nishikawa A, Tonozuka T J Biol Chem. 2015 Sep 1. pii: jbc.M115.680942. PMID:26330557^[1]

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