Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan.
Microbiology (Reading). 2010 May;156(Pt 5):1538-1546. doi: 10.1099/mic.0.037499-0. Epub 2010 Feb 4.
scyllo-Inositol (SI) is a stereoisomer of inositol whose catabolism has not been characterized in bacteria. We found that Bacillus subtilis 168 was able to grow using SI as its sole carbon source and that this growth was dependent on a functional iol operon for catabolism of myo-inositol (MI; another inositol isomer, which is abundant in nature). Previous studies elucidated the MI catabolic pathway in B. subtilis as comprising multiple stepwise reactions catalysed by a series of Iol enzymes. The first step of the pathway converts MI to scyllo-inosose (SIS) and involves the MI dehydrogenase IolG. Since IolG does not act on SI, we suspected that there could be another enzyme converting SI into SIS, namely an SI dehydrogenase. Within the whole genome, seven genes paralogous to iolG have been identified and two of these, iolX and iolW (formerly known as yisS and yvaA, respectively), were selected as candidate genes for the putative SI dehydrogenase since they were both prominently expressed when B. subtilis was grown on medium containing SI. iolX and iolW were cloned in Escherichia coli and both were shown to encode a functional enzyme, revealing the two distinct SI dehydrogenases in B. subtilis. Since inactivation of iolX impaired growth with SI as the carbon source, IolX was identified as a catabolic enzyme required for SI catabolism and it was shown to be NAD(+) dependent. The physiological role of IolW remains unclear, but it may be capable of producing SI from SIS with NADPH oxidation.
肌醇（MI）是一种立体异构体，其在细菌中的分解代谢尚未被描述。我们发现枯草芽孢杆菌 168 可以利用肌醇作为唯一的碳源进行生长，并且这种生长依赖于功能性的 iol 操纵子来分解肌醇（MI；另一种在自然界中含量丰富的肌醇异构体）。先前的研究阐明了枯草芽孢杆菌中的 MI 分解代谢途径，该途径由一系列 Iol 酶催化的多个逐步反应组成。该途径的第一步将 MI 转化为 scyllo-肌醇（SIS），并涉及 MI 脱氢酶 IolG。由于 IolG 不能作用于 SI，我们怀疑可能存在另一种将 SI 转化为 SIS 的酶，即 SI 脱氢酶。在整个基因组中，已经鉴定出与 iolG 具有同源性的七个基因，其中两个基因iolX 和 iolW（以前分别称为 yisS 和 yvaA）被选为推测的 SI 脱氢酶的候选基因，因为它们在枯草芽孢杆菌生长在含有 SI 的培养基中时都被显著表达。iolX 和 iolW 在大肠杆菌中被克隆，两者都编码一种功能性酶，揭示了枯草芽孢杆菌中两种不同的 SI 脱氢酶。由于 iolX 的失活会损害以 SI 为碳源的生长，因此 IolX 被鉴定为 SI 分解代谢所需的分解代谢酶，并且它依赖 NAD(+)。IolW 的生理作用尚不清楚，但它可能能够利用 NADPH 氧化从 SIS 产生 SI。
