RESUMO
The Arc (anoxic redox control) two-component signal transduction system, consisting of the ArcB sensor kinase and the ArcA response regulator, allows adaptive responses of Escherichia coli to changes of O(2) availability. The arcA gene was previously known as the dye gene because null mutants were growth sensitive to the photosensitizer redox dyes toluidine blue and methylene blue, a phenotype whose molecular basis still remains elusive. In this study we report that the toluidine blue O (TBO) effect on the arc mutants is light independent and observed only during aerobic growth conditions. Moreover, 16 suppressor mutants with restored growth were generated and analyzed. Thirteen of those possessed insertion elements upstream of the cydAB operon, rendering its expression ArcA independent. Also, it was found that, in contrast to cythocrome d, cythocrome o was not able to confer toluidine blue resistance to arc mutants, thereby representing an intriguing difference between the two terminal oxidases. Finally, a mechanism for TBO sensitivity and resistance is discussed.
Assuntos
Proteínas da Membrana Bacteriana Externa/genética , Grupo dos Citocromos b/metabolismo , Grupo dos Citocromos d/metabolismo , Citocromos/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/efeitos dos fármacos , Escherichia coli/crescimento & desenvolvimento , Proteínas Repressoras/genética , Cloreto de Tolônio/farmacologia , Anaerobiose , Proteínas da Membrana Bacteriana Externa/metabolismo , Sequência de Bases , Carotenoides/metabolismo , Catalase/metabolismo , Corantes/farmacologia , Grupo dos Citocromos b/genética , Grupo dos Citocromos d/genética , Citocromos/genética , Escuridão , Complexo de Proteínas da Cadeia de Transporte de Elétrons/genética , Escherichia coli/genética , Escherichia coli/metabolismo , Proteínas de Escherichia coli/genética , Regulação Bacteriana da Expressão Gênica/efeitos dos fármacos , Regulação Bacteriana da Expressão Gênica/genética , Regulação Bacteriana da Expressão Gênica/efeitos da radiação , Glucose/farmacologia , Luz , Dados de Sequência Molecular , Mutação/genética , Oxirredutases/genética , Regiões Promotoras Genéticas/genética , Espécies Reativas de Oxigênio/metabolismo , Proteínas Repressoras/metabolismo , Homologia de Sequência do Ácido Nucleico , Superóxido Dismutase/metabolismoRESUMO
Escherichia coli senses and signals anoxic or low redox conditions in its growth environment by the Arc two-component system. Under anaerobic conditions, the ArcB sensor kinase autophosphorylates and transphosphorylates ArcA, a global transcriptional regulator that controls the expression of numerous operons involved in respiratory or fermentative metabolism. Under aerobic conditions, the kinase activity of ArcB is inhibited by the quinone electron carriers that act as direct negative signals. Here, we show that the molecular mechanism of kinase silencing involves the oxidation of two cytosol-located redox-active cysteine residues that participate in intermolecular disulfide bond formation, a reaction in which the quinones provide the source of oxidative power. Thus, a pivotal link in the Arc signal transduction pathway connecting the redox state of the quinone pool to the transcriptional apparatus is elucidated.