Lenz O, Friedrich B
Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestrasse 117, 10115 Berlin, Germany.
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12474-9. doi: 10.1073/pnas.95.21.12474.
Oxidation of molecular hydrogen catalyzed by [NiFe] hydrogenases is a widespread mechanism of energy generation among prokaryotes. Biosynthesis of the H2-oxidizing enzymes is a complex process subject to positive control by H2 and negative control by organic energy sources. In this report we describe a novel signal transduction system regulating hydrogenase gene (hox) expression in the proteobacterium Alcaligenes eutrophus. This multicomponent system consists of the proteins HoxB, HoxC, HoxJ*, and HoxA. HoxB and HoxC share characteristic features of dimeric [NiFe] hydrogenases and form the putative H2 receptor that interacts directly or indirectly with the histidine protein kinase HoxJ*. A single amino acid substitution (HoxJG422S) in a conserved C-terminal glycine-rich motif of HoxJ resulted in a loss of H2-dependent signal transduction and a concomitant block in autophosphorylating activity, suggesting that autokinase activity is essential for the response to H2. Whereas deletions in hoxB or hoxC abolished hydrogenase synthesis almost completely, the autokinase-deficient strain maintained high-level hox gene expression, indicating that the active sensor kinase exerts a negative effect on hox gene expression in the absence of H2. Substitutions of the conserved phosphoryl acceptor residue Asp55 in the response regulator HoxA (HoxAD55E and HoxAD55N) disrupted the H2 signal-transduction chain. Unlike other NtrC-like regulators, the altered HoxA proteins still allowed high-level transcriptional activation. The data presented here suggest a model in which the nonphosphorylated form of HoxA stimulates transcription in concert with a yet unknown global energy-responsive factor.
由[NiFe]氢化酶催化的分子氢氧化是原核生物中广泛存在的能量产生机制。H2氧化酶的生物合成是一个复杂的过程，受到H2的正调控和有机能源的负调控。在本报告中，我们描述了一种调节嗜糖产碱杆菌中氢化酶基因（hox）表达的新型信号转导系统。这个多组分系统由HoxB、HoxC、HoxJ和HoxA蛋白组成。HoxB和HoxC具有二聚体[NiFe]氢化酶的特征，形成假定的H2受体，它直接或间接与组氨酸蛋白激酶HoxJ相互作用。HoxJ保守的C末端富含甘氨酸基序中的单个氨基酸取代（HoxJG422S）导致H2依赖性信号转导丧失，并伴随自磷酸化活性受阻，这表明自激酶活性对于对H2的反应至关重要。虽然hoxB或hoxC的缺失几乎完全消除了氢化酶的合成，但自激酶缺陷菌株保持高水平的hox基因表达，这表明在没有H2的情况下，活性传感器激酶对hox基因表达产生负面影响。反应调节因子HoxA中保守的磷酸受体残基Asp55的取代（HoxAD55E和HoxAD55N）破坏了H2信号转导链。与其他NtrC样调节因子不同，改变后的HoxA蛋白仍然允许高水平的转录激活。这里呈现的数据提出了一个模型，其中HoxA的非磷酸化形式与一个未知的全局能量响应因子协同刺激转录。
