Stewart V
Section of Microbiology, University of California, 1 Shields Avenue, Davis, CA 95616-8665, USA.
Biochem Soc Trans. 2003 Feb;31(Pt 1):1-10. doi: 10.1042/bst0310001.
Nitrate and nitrite are efficient respiratory oxidants for anaerobic growth. In Escherichia coli, the homologous nitrate reductase (Nar) two-component regulatory systems NarX-NarL and NarQ-NarP collaborate to control anaerobic respiratory gene expression in response to nitrate and nitrite. Several other species classified in the gamma and beta subdivisions of the proteobacteria contain only a single Nar two-component regulatory pair. This raises questions concerning the physiology of anaerobic respiration as well as the evolution, function and cross-regulation of two-component regulatory systems. Here, I focus on the sensor histidine kinases NarX and NarQ, and present a comparison of the deduced NarX and NarQ primary sequences from a broad sampling of proteobacteria. This comparison defines shared features, including a large central region of unknown function that appears to be unique to this family of sensor kinases. I then consider the phylogenetic distribution of narX and narQ genes in relation to anaerobic respiratory enzyme repertoire and physiological function. One noteworthy observation is that narXL genes are specifically associated with the structural genes for membrane-bound nitrate reductase, narGHJI, whereas organization and linkage of the narQ and narP genes is quite variable. I conclude with some speculative thoughts on the evolutionary and functional divergence of the NarX-NarL and NarQ-NarP regulatory systems. Overall, this analysis aims to provide a basis for future hypothesis and experimentation in this area.
硝酸盐和亚硝酸盐是厌氧生长的有效呼吸氧化剂。在大肠杆菌中，同源硝酸盐还原酶（Nar）双组分调节系统NarX-NarL和NarQ-NarP协同作用，以响应硝酸盐和亚硝酸盐来控制厌氧呼吸基因的表达。在变形菌门的γ和β亚类中分类的其他几个物种仅包含单个Nar双组分调节对。这就引发了关于厌氧呼吸生理学以及双组分调节系统的进化、功能和交叉调节的问题。在这里，我重点关注传感组氨酸激酶NarX和NarQ，并对来自广泛采样的变形菌门的推导NarX和NarQ一级序列进行比较。这种比较定义了共同特征，包括一个功能未知的大中心区域，该区域似乎是这个传感激酶家族所特有的。然后，我考虑了narX和narQ基因的系统发育分布与厌氧呼吸酶库和生理功能的关系。一个值得注意的观察结果是，narXL基因与膜结合硝酸盐还原酶narGHJI的结构基因特异性相关，而narQ和narP基因的组织和连锁则变化很大。我以对NarX-NarL和NarQ-NarP调节系统的进化和功能差异的一些推测性思考作为结论。总体而言，该分析旨在为该领域未来的假设和实验提供基础。
