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 | ResearchHub
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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
Hiromi Yoshida, Akihide Yoshihara, Misa Teraoka, Ken Izumori, Shigehiro Kamitori
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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.
