Abstract
The reason for the existence of complex sensor kinases is little understood but thought to lie in the capacity to respond to multiple signals. The complex, seven-domain sensor kinase TodS controls in concert with the TodT response regulator the expression of the toluene dioxygenase pathway in Pseudomonas putida F1 and DOT-T1E. We have previously shown that some aromatic hydrocarbons stimulate TodS activity whereas others behave as antagonists. We show here that TodS responds in addition to the oxidative agent menadione. Menadione but no other oxidative agent tested inhibited TodS activity in vitro and reduced PtodX expression in vivo. The menadione signal is incorporated by a cysteine-dependent mechanism. The mutation of the sole conserved cysteine of TodS (C320) rendered the protein insensitive to menadione. We evaluated the mutual opposing effects of toluene and menadione on TodS autophosphorylation. In the presence of toluene, menadione reduced TodS activity whereas toluene did not stimulate activity in the presence of menadione. It was shown by others that menadione increases expression of glucose metabolism genes. The opposing effects of menadione on glucose and toluene metabolism may be partially responsible for the interwoven regulation of both catabolic pathways. This work provides mechanistic detail on how complex sensor kinases integrate different types of signal molecules.
Highlights
Two-component systems (TCSs) are a major bacterial signal transduction mechanism and regulate virtually all types of cellular processes (Galperin, 2005; Mascher et al, 2006; Krell et al, 2010)
We have addressed this question using the complex TodS/TodT TCS of Pseudomonas putida DOT-T1E, which was shown to modulate the expression from promoter PtodX that controls the genes of the toluene dioxygenase pathway (TOD) for the metabolization of benzene, toluene and ethylbenzene (Zylstra and Gibson, 1989; Lau et al, 1997; Mosqueda et al, 1999)
Apart from aromatic hydrocarbons, TodS activity is modulated by menadione via a cysteine dependent mechanism
Summary
Two-component systems (TCSs) are a major bacterial signal transduction mechanism and regulate virtually all types of cellular processes (Galperin, 2005; Mascher et al, 2006; Krell et al, 2010). The basic components of a TCS are a sensor kinase and a response regulator. There are sensor kinases that possess multiple copies of the same domain type or harbour additional domains like histidine containing phosphotransfer domains (Krell et al, 2010). This complexity in architecture is frequently reflected in a more complex mechanism as many of these TCS employ a His1-Asp1-His2-Asp phosphorelay instead of a simple His-Asp phosphoryl-transfer of the prototypal system (Pena-Sandoval et al, 2005; Zhang and Shi, 2005; Cock and Whitworth, 2007; Busch et al, 2009).
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