Abstract
The energy taxis receptor Aer, in Escherichia coli, senses changes in the redox state of the electron transport system via an flavin adenine dinucleotide cofactor bound to a PAS domain. The PAS domain (a sensory domain named after three proteins Per, ARNT and Sim, where it was first identified) is thought to interact directly with the Aer HAMP domain to transmit this signal to the highly conserved domain (HCD) found in chemotaxis receptors. An apparent energy taxis system in Campylobacter jejuni is composed of two proteins, CetA and CetB, that have the domains of Aer divided between them. CetB has a PAS domain, while CetA has a predicted transmembrane region, HAMP domain and the HCD. In this study, we examined the expression of cetA and cetB and the biochemical properties of the proteins they encode. cetA and cetB are co-transcribed independently of the flagellar regulon. CetA has two transmembrane helices in a helical hairpin while CetB is a peripheral membrane protein tightly associated with the membrane. CetB levels are CetA dependent. Additionally, we demonstrated that both CetA and CetB participate in complexes, including a likely CetB dimer and a complex that may include both CetA and CetB. This study provides a foundation for further characterization of signal transduction mechanisms within CetA/CetB.
Highlights
Motile bacteria alter the direction in which they swim based on changes in the local environment
The energy taxis receptor Aer, in Escherichia coli, senses changes in the redox state of the electron transport system via an flavin adenine dinucleotide cofactor bound to a PAS domain
The PAS domain is thought to interact directly with the Aer HAMP domain to transmit this signal to the highly conserved domain (HCD) found in chemotaxis receptors
Summary
Motile bacteria alter the direction in which they swim based on changes in the local environment. These changes can be sensed directly in classical chemotaxis, where changes in the local concentration of a stimulus. Changes in the local environment can be sensed indirectly by monitoring energy-generating processes within the cell. Energy taxis behaviours include some forms of aerotaxis, phototaxis, taxis to electron acceptors and even chemotaxis in those cases where the bacteria sense chemicals based on changes in energy generation resulting from their metabolism (Taylor and Zhulin, 1998; Taylor et al, 1999; Alexandre et al, 2004)
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