Department of Chemical Engineering, University of Washington, Seattle, Washington 98195-2180, USA.
J Bacteriol. 2011 Nov;193(21):6032-8. doi: 10.1128/JB.05367-11. Epub 2011 Aug 26.
In Gram-negative methylotrophic bacteria, the first step in methylotrophic growth is the oxidation of methanol to formaldehyde in the periplasm by methanol dehydrogenase. In most organisms studied to date, this enzyme consists of the MxaF and MxaI proteins, which make up the large and small subunits of this heterotetrameric enzyme. The Methylobacterium extorquens AM1 genome contains two homologs of MxaF, XoxF1 and XoxF2, which are ∼50% identical to MxaF and ∼90% identical to each other. It was previously reported that xoxF is not required for methanol growth in M. extorquens AM1, but here we show that when both xoxF homologs are absent, strains are unable to grow in methanol medium and lack methanol dehydrogenase activity. We demonstrate that these defects result from the loss of gene expression from the mxa promoter and suggest that XoxF is part of a complex regulatory cascade involving the 2-component systems MxcQE and MxbDM, which are required for the expression of the methanol dehydrogenase genes.
在革兰氏阴性甲基营养细菌中，甲基营养生长的第一步是甲醇脱氢酶将甲醇在周质中氧化为甲醛。在迄今为止研究的大多数生物体中，该酶由 MxaF 和 MxaI 蛋白组成，这两种蛋白构成了这种异四聚体酶的大亚基和小亚基。甲基杆菌扩展 AM1 基因组包含两个 MxaF 的同源物，XoxF1 和 XoxF2，它们与 MxaF 的相似度约为 50%，彼此的相似度约为 90%。先前的研究报告称，xoxF 不是甲基杆菌扩展 AM1 中甲醇生长所必需的，但在这里我们表明，当两个 xoxF 同源物都缺失时，菌株无法在甲醇培养基中生长并且缺乏甲醇脱氢酶活性。我们证明这些缺陷是由于 mxa 启动子的基因表达丧失所致，并表明 XoxF 是涉及 2 组分系统 MxcQE 和 MxbDM 的复杂调控级联的一部分，这对于甲醇脱氢酶基因的表达是必需的。
