title: Structure of l-rhamnose isomerase in complex with l-rhamnopyranose demonstrates the sugar-ring opening mechanism and the role of a substrate sub-binding site.
abstract: l-Rhamnose isomerase (l-RhI) catalyzes the reversible isomerization of l-rhamnose to l-rhamnulose. Previously determined X-ray structures of l-RhI showed a hydride-shift mechanism for the isomerization of substrates in a linear form, but the mechanism for opening of the sugar-ring is still unclear. To elucidate this mechanism, we determined X-ray structures of a mutant l-RhI in complex with l-rhamnopyranose and d-allopyranose. Results suggest that a catalytic water molecule, which acts as an acid/base catalyst in the isomerization reaction, is likely to be involved in pyranose-ring opening, and that a newly found substrate sub-binding site in the vicinity of the catalytic site may recognize different anomers of substrates.
authors.affiliation: Life Science Research Center and Faculty of Medicine, Kagawa University, 1750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Yoshida
authors.forename: Akihide
authors.initials: A
authors.lastname: Yoshihara
authors.forename: Misa
authors.initials: M
authors.lastname: Teraoka
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamashita
authors.forename: Ken
authors.initials: K
authors.lastname: Izumori
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Kamitori
keywords: D327N, mutant P. stutzeril-RhI, with a substitution of Asp327 with Asn; E. coli, Escherichia coli; H101N, mutant P. stutzeril-RhI, with a substitution of H101 with Asn; P. stutzeri, Pseudomonas stutzeri; Pseudomonas stutzeri; RNS, l-rhamnose in a linear form; Rare sugar; Sugar-ring opening mechanism; X-ray structure; l-RhI, l-rhamnose isomerase; l-Rhamnose isomerase; α-APS, α-d-allopyranose; α-RPS, α-l-rhamnopyranose; β-RPS, β-l-rhamnopyranose