Structural insights into the catalytic reaction that is involved in the reorientation of Trp238 at the substrate-binding site in GH13 dextran glucosidase
Kobayashi, M., Saburi, W., Nakatsuka, D., Hondoh, H., Kato, K., Okuyama, M., Mori, H., Kimura, A., Yao, M.(2015) FEBS Lett 589: 484-489
- PubMed: 25595454 
- DOI: https://doi.org/10.1016/j.febslet.2015.01.005
- Primary Citation of Related Structures:  
4WLC, 4XB3 - PubMed Abstract: 
Streptococcus mutans dextran glucosidase (SmDG) belongs to glycoside hydrolase family 13, and catalyzes both the hydrolysis of substrates such as isomaltooligosaccharides and subsequent transglucosylation to form α-(1→6)-glucosidic linkage at the substrate non-reducing ends. Here, we report the 2.4Å resolution crystal structure of glucosyl-enzyme intermediate of SmDG. In the obtained structure, the Trp238 side-chain that constitutes the substrate-binding site turned away from the active pocket, concurrently with conformational changes of the nucleophile and the acid/base residues. Different conformations of Trp238 in each reaction stage indicated its flexibility. Considering the results of kinetic analyses, such flexibility may reflect a requirement for the reaction mechanism of SmDG.
Organizational Affiliation: 
Graduate School of Life Science, Hokkaido University, Kita-10, Nishi-8, Kita-ku, Sapporo 060-0810, Japan.