Nishijyo T, Haas D, Itoh Y
Division of Applied Microbiology, National Food Research Institute, Ministry of Agriculture, Forestry and Fisheries, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8642, Japan.
Mol Microbiol. 2001 May;40(4):917-31. doi: 10.1046/j.1365-2958.2001.02435.x.
A novel two-component system, CbrA-CbrB, was discovered in Pseudomonas aeruginosa; cbrA and cbrB mutants of strain PAO were found to be unable to use several amino acids (such as arginine, histidine and proline), polyamines and agmatine as sole carbon and nitrogen sources. These mutants were also unable to use, or used poorly, many other carbon sources, including mannitol, glucose, pyruvate and citrate. A 7 kb EcoRI fragment carrying the cbrA and cbrB genes was cloned and sequenced. The cbrA and cbrB genes encode a sensor/histidine kinase (Mr 108 379, 983 residues) and a cognate response regulator (Mr 52 254, 478 residues) respectively. The amino-terminal half (490 residues) of CbrA appears to be a sensor membrane domain, as predicted by 12 possible transmembrane helices, whereas the carboxy-terminal part shares homology with the histidine kinases of the NtrB family. The CbrB response regulator shows similarity to the NtrC family members. Complementation and primer extension experiments indicated that cbrA and cbrB are transcribed from separate promoters. In cbrA or cbrB mutants, as well as in the allelic argR9901 and argR9902 mutants, the aot-argR operon was not induced by arginine, indicating an essential role for this two-component system in the expression of the ArgR-dependent catabolic pathways, including the aruCFGDB operon specifying the major aerobic arginine catabolic pathway. The histidine catabolic enzyme histidase was not expressed in cbrAB mutants, even in the presence of histidine. In contrast, proline dehydrogenase, responsible for proline utilization (Pru), was expressed in a cbrB mutant at a level comparable with that of the wild-type strain. When succinate or other C4-dicarboxylates were added to proline medium at 1 mM, the cbrB mutant was restored to a Pru+ phenotype. Such a succinate-dependent Pru+ property was almost abolished by 20 mM ammonia. In conclusion, the CbrA-CbrB system controls the expression of several catabolic pathways and, perhaps together with the NtrB-NtrC system, appears to ensure the intracellular carbon: nitrogen balance in P. aeruginosa.
在铜绿假单胞菌中发现了一种新型双组分系统CbrA-CbrB；PAO菌株的cbrA和cbrB突变体被发现无法利用几种氨基酸（如精氨酸、组氨酸和脯氨酸）、多胺和胍丁胺作为唯一的碳源和氮源。这些突变体也无法利用或很少利用许多其他碳源，包括甘露醇、葡萄糖、丙酮酸和柠檬酸盐。携带cbrA和cbrB基因的一个7 kb的EcoRI片段被克隆并测序。cbrA和cbrB基因分别编码一个传感器/组氨酸激酶（分子量108 379，983个氨基酸残基）和一个同源反应调节因子（分子量52 254，478个氨基酸残基）。如通过12个可能的跨膜螺旋所预测的，CbrA的氨基末端一半（490个氨基酸残基）似乎是一个传感器膜结构域，而羧基末端部分与NtrB家族的组氨酸激酶具有同源性。CbrB反应调节因子与NtrC家族成员相似。互补和引物延伸实验表明，cbrA和cbrB是从各自的启动子转录的。在cbrA或cbrB突变体以及等位基因argR9901和argR9902突变体中，aot-argR操纵子不会被精氨酸诱导，这表明该双组分系统在依赖精氨酸调节蛋白（ArgR）的分解代谢途径（包括指定主要需氧精氨酸分解代谢途径的aruCFGDB操纵子）的表达中起关键作用。组氨酸分解代谢酶组氨酸酶在cbrAB突变体中不表达，即使在有组氨酸存在的情况下也是如此。相反，负责脯氨酸利用（Pru）的脯氨酸脱氢酶在cbrB突变体中的表达水平与野生型菌株相当。当向脯氨酸培养基中添加1 mM琥珀酸或其他C4-二羧酸时，cbrB突变体恢复为Pru+表型。这种依赖琥珀酸的Pru+特性几乎被20 mM氨消除。总之，CbrA-CbrB系统控制着几种分解代谢途径的表达，并且可能与NtrB-NtrC系统一起，似乎确保了铜绿假单胞菌细胞内的碳：氮平衡。
