Structural highlights
Publication Abstract from PubMedSugar beet alpha-glucosidase (SBG), a member of glycoside hydrolase family 31, shows exceptional long-chain specificity, exhibiting higher kcat/Kms for longer maltooligosaccharides. However, its amino acid sequence is similar to other short-chain-specific alpha-glucosidases. To gain structural insights into the long-chain-substrate recognition of SBG, a crystal structure complex with the pseudotetrasaccharide, acarbose, was determined at 1.7 A resolution. The active site pocket of SBG was formed by a (beta/alpha)8 barrel domain and a long loop (the N-loop) bulging from the N-terminal domain similar to other related enzymes. Two residues, Phe236 and Asn237 in the N-loop were important for the long-chain specificity. Kinetic analysis of an Asn237 mutant enzyme and a previous study of a Phe236 mutant enzyme demonstrated that these residues create subsites +2 and +3. The structure also indicated that Phe236 and Asn237 guided the reducing end of long substrates to subdomain b2, which is an additional element inserted into the (beta/alpha)8 barrel domain. Subdomain b2 of SBG included Ser497, which was identified as the residue at subsite +4 by site-directed mutagenesis. Molecular basis for the recognition of long-chain substrates by plant alpha-glucosidase.,Tagami T, Yamashita K, Okuyama M, Mori H, Yao M, Kimura A J Biol Chem. 2013 May 16. PMID:23687304[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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