Altering the substrate chain-length specificity of an alpha-glucosidase |
| |
Authors: | Noguchi Akio Nakayama Toru Hemmi Hisashi Nishino Tokuzo |
| |
Affiliation: | Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 07 Aza Aobayama Aramaki, Aoba-ku, Sendai-shi, Miyagi-ken 980-8579, Japan. |
| |
Abstract: | Dextran glucosidases show high sequence identity (50%) to Bacillus sp. SAM1606 alpha-glucosidase, which is more specific for short-chain substrates. Sequence comparison of these enzymes as well as molecular modeling studies predicted that the extension of loop 4 of the (beta/alpha)(8)-barrel fold may be responsible for the narrower specificity of SAM1606 alpha-glucosidase with respect to substrate chain length. Indeed, deletion mutants of SAM1606 alpha-glucosidase that lack this extension showed higher relative activities toward dextran and long-chain isomaltooligosaccharides. Kinetic and thermodynamic analyses of oligosaccharide hydrolysis catalyzed by SAM1606 alpha-glucosidase and its deletion mutants suggested that the loss of such extension(s) in loop 4 should energetically destabilize the Michaelis complexes with long-chain substrates to result in smaller differences between the activation free energies for the enzymatic hydrolyses of isomaltoheptaose and isomaltose than those observed for the wild-type enzyme. This is the reason that dextran glucosidase, whose loop 4 is shorter in length, shows broader substrate chain-length specificity than does SAM1606 alpha-glucosidase. |
| |
Keywords: | α-Glucosidase Dextran glucosidase Isomaltase Exodextranase Substrate specificity Isomaltooligosaccharides Glycosyl hydrolase family α-Amylase family Chain length |
本文献已被 ScienceDirect PubMed 等数据库收录! |
|