Life Science Research Center and Faculty of Medicine, Kagawa University, 1750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793, Japan.
FEBS Open Bio. 2012 Dec 7;3:35-40. doi: 10.1016/j.fob.2012.11.008. Print 2013.
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.
l-鼠李糖异构酶（l-RhI）催化 l-鼠李糖可逆异构化为 l-鼠李酮糖。先前确定的 l-RhI 的 X 射线结构显示出底物在直线形式下的异构化的氢化物转移机制，但糖环的打开机制仍不清楚。为了阐明这一机制，我们确定了与 l-鼠李吡喃糖和 d-阿洛吡喃糖复合物的突变 l-RhI 的 X 射线结构。结果表明，催化异构化反应的酸/碱催化剂作用的一个催化水分子可能参与吡喃糖环的打开，并且在催化位点附近新发现的底物亚结合位点可能识别不同的底物异头物。
