Myronova Natalia, Kitmitto Ashraf, Collins Richard F, Miyaji Aki, Dalton Howard
Department of Biological Sciences, University of Warwick, Coventry CV4 8EZ, UK.
Biochemistry. 2006 Oct 3;45(39):11905-14. doi: 10.1021/bi061294p.
The oxidation of methane to methanol in methanotrophs is catalyzed by the enzyme methane monooxygenase (MMO). Two distinct forms of this enzyme exist, a soluble cytoplasmic MMO (sMMO) and a membrane-bound particulate form (pMMO). The active protein complex termed pMMO-C was purified recently from Methylococcus capsulatus (Bath). The complex consists of pMMO hydroxylase and an additional component pMMO-R, which was proposed to be the reductase for the pMMO complex. Further study of this complex has led here to the proposal that the pMMO-R is in fact methanol dehydrogenase, the subsequent enzyme in the methane oxidation pathway by methanotrophs. We describe here the biochemical and biophysical characterization of a stable purified complex of pMMO hydroxylase (pMMO-H) with methanol dehydrogenase (MDH) and report the first three-dimensional (3D) structure, determined by cryoelectron microscopy and single particle analysis to approximately 16 A resolution. The 3D structure reported here provides the first insights into the supramolecular organization of pMMO with MDH. These studies of pMMO-MDH complexes have provided further understanding of the structural basis for the particular functions of the enzymes in this system which might also be of relevance to the complete process of methane oxidation by methanotrophs under high copper concentration in the environment.
甲烷氧化菌中甲烷向甲醇的氧化由甲烷单加氧酶（MMO）催化。该酶存在两种不同形式，一种是可溶性细胞质MMO（sMMO），另一种是膜结合颗粒形式（pMMO）。最近从荚膜甲基球菌（巴斯德菌株）中纯化出了被称为pMMO-C的活性蛋白复合物。该复合物由pMMO羟化酶和另一种成分pMMO-R组成，有人提出pMMO-R是pMMO复合物的还原酶。对该复合物的进一步研究使我们在此提出，pMMO-R实际上是甲醇脱氢酶，它是甲烷氧化菌甲烷氧化途径中的后续酶。我们在此描述了pMMO羟化酶（pMMO-H）与甲醇脱氢酶（MDH）形成的稳定纯化复合物的生化和生物物理特性，并报告了通过冷冻电子显微镜和单颗粒分析确定的约16埃分辨率的首个三维（3D）结构。此处报道的3D结构首次揭示了pMMO与MDH的超分子组织情况。对pMMO-MDH复合物的这些研究进一步了解了该系统中酶特定功能的结构基础，这可能也与环境中高铜浓度下甲烷氧化菌甲烷氧化的完整过程相关。
