A novel redox-sensing histidine kinase controls the anaerobic degradation of aromatic compounds in some bacteria

The group of Dr. Eduardo Díaz in collaboration with the group of Prof. Javier Cañada, both at the Centro de Investigaciones Biológicas (CSIC), have identified and characterized a multidomain protein that expands the functional diversity of redox sensing kinases towards the control of carbon catabolite repression (CCR), a phenomenon that allows the selective assimilation of a preferred compound among a mixture of several carbon sources. The results of this work have been published in mBio.

Two-component signal transduction systems are widespread in prokaryotes and play key roles in adaptation to environmental changes. These systems comprise a sensor histidine kinase and its cognate response regulator, and some have evolved to sense and convert redox signals into regulatory outputs that allow bacteria to adapt to the altered redox environment.

In this work, the authors show that the AccS sensor kinase mediates the activation of the AccR master regulator involved in CCR of the anaerobic catabolism of aromatic compounds in the beta-proteobacterium Azoarcus sp. CIB. In vitro assays with purified AccS’ (a truncated AccS protein that contains only the soluble C-terminal autokinase module) revealed its autophosphorylation, phosphotransfer from AccS’~P to the Asp60 residue of AccR, and the phosphatase activity toward its phosphorylated response regulator. Oxidized quinones, e.g. ubiquinone 0 and menadione, switched the AccS’ autokinase activity off, and three conserved Cys residues, which are not essential for catalysis, are involved in such inhibition. Therefore, AccS’ seems to have a thiol-based redox switch that is modulated by the redox state of the quinone pool of the bacterial cell.

The AccSR system from Azoarcus sp. CIB is conserved in several beta-proteobacteria and, therefore, it becomes a new cell redox state-sensing two-component regulatory system that could play a more general role controlling the global metabolic state in this group of proteobacteria.  

Reference: "A Novel Redox-Sensing Histidine Kinase that Controls Carbon Catabolite Repression in Azoarcus sp. CIB". J. Andrés Valderrama, Helena Gómez-Álvarez, Zaira Martín-Moldes, M. Álvaro Berbís, F. Javier Cañada, Gonzalo Durante-Rodríguez, Eduardo Díaz. mBio. DOI: 10.1128/mBio.00059-19