Department of Chemistry, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5C9.
Biochem J. 2010 Dec 1;432(2):237-47. doi: 10.1042/BJ20101079.
Inositol dehydrogenase from Bacillus subtilis (BsIDH) is a NAD+-dependent enzyme that catalyses the oxidation of the axial hydroxy group of myo-inositol to form scyllo-inosose. We have determined the crystal structures of wild-type BsIDH and of the inactive K97V mutant in apo-, holo- and ternary complexes with inositol and inosose. BsIDH is a tetramer, with a novel arrangement consisting of two long continuous β-sheets, formed from all four monomers, in which the two central strands are crossed over to form the core of the tetramer. Each subunit in the tetramer consists of two domains: an N-terminal Rossmann fold domain containing the cofactor-binding site, and a C-terminal domain containing the inositol-binding site. Structural analysis allowed us to determine residues important in cofactor and substrate binding. Lys97, Asp172 and His176 are the catalytic triad involved in the catalytic mechanism of BsIDH, similar to what has been proposed for related enzymes and short-chain dehydrogenases. Furthermore, a conformational change in the nicotinamide ring was observed in some ternary complexes, suggesting hydride transfer to the si-face of NAD+. Finally, comparison of the structure and sequence of BsIDH with other putative inositol dehydrogenases allowed us to differentiate these enzymes into four subfamilies based on six consensus sequence motifs defining the cofactor- and substrate-binding sites.
枯草芽孢杆菌肌醇脱氢酶（BsIDH）是一种 NAD+依赖的酶，可催化肌醇轴向羟基的氧化，形成表肌醇。我们已解析了野生型 BsIDH 及无活性突变体 K97V 的晶体结构，其分别处于 apo、holo 和与肌醇和表肌醇形成的三元复合物状态。BsIDH 是一个四聚体，由两个由所有四个单体形成的长连续β-折叠组成，其中两条中心链交叉形成四聚体的核心。四聚体中的每个亚基由两个结构域组成：一个含有辅因子结合位点的 N 端 Rossmann 折叠结构域，和一个含有肌醇结合位点的 C 端结构域。结构分析确定了与辅因子和底物结合相关的重要残基。Lys97、Asp172 和 His176 是 BsIDH 催化机制中的催化三联体，与相关酶和短链脱氢酶中的催化三联体相似。此外，在一些三元复合物中观察到烟酰胺环的构象变化，表明氢化物向 NAD+的 si-面转移。最后，将 BsIDH 的结构和序列与其他假定的肌醇脱氢酶进行比较，使我们能够基于定义辅因子和底物结合位点的六个共识序列基序，将这些酶分为四个亚家族。
