scyllo-Inositol (SI) is a stereoisomer of inositol whose catabolism has not been characterized in bacteria. We found thatBacillus subtilis168 was able to grow using SI as its sole carbon source and that this growth was dependent on a functionalioloperon for catabolism ofmyo-inositol (MI; another inositol isomer, which is abundant in nature). Previous studies elucidated the MI catabolic pathway inB. subtilisas comprising multiple stepwise reactions catalysed by a series of Iol enzymes. The first step of the pathway converts MI toscyllo-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 toiolGhave been identified and two of these,iolXandiolW(formerly known asyisSandyvaA, respectively), were selected as candidate genes for the putative SI dehydrogenase since they were both prominently expressed whenB. subtiliswas grown on medium containing SI.iolXandiolWwere cloned inEscherichia coliand both were shown to encode a functional enzyme, revealing the two distinct SI dehydrogenases inB. subtilis. Since inactivation ofiolXimpaired 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.
scyllo-肌醇(SI)是肌醇的立体异构体,其在细菌中的分解代谢尚未被表征。我们发现
Bacillus subtilis168能够利用SI作为其唯一的碳源生长,并且该生长依赖于功能性的
iol操纵子来代谢
myo-肌醇(MI;另一种在自然界中丰富的肌醇异构体)。以前的研究阐明了
B. subtilis中MI代谢途径由一系列Iol酶催化的多步反应组成。途径的第一步将MI转化为
scyllo-肌醇糖(SIS),并涉及MI脱氢酶IolG。由于IolG不作用于SI,我们怀疑可能存在另一种酶将SI转化为SIS,即SI脱氢酶。在整个
基因组中,已经鉴定出与
iolG同源的七个
基因,其中两个,
iolX和
iolW(以前分别称为
yisS和
yvaA),被选为假定的SI脱氢酶的候选
基因,因为它们在含有SI的
培养基中生长时都表达明显。
iolX和
iolW被克隆到
Escherichia coli中,并且两者都被证明编码一种功能性酶,揭示了
B. subtilis中两种不同的SI脱氢酶。由于
iolX失活会影响以SI为碳源的生长,因此确定了IolX作为SI代谢所需的代谢酶,并且它被证明是
NAD+依赖的。IolW的生理作用尚不清楚,但它可能能够通过
NADPH氧化从SIS产生SI。