BioQuant Insitute, Im Neuenheimer Feld 267, 69120 Heidelberg, Germany
Zentrum fuer Molekulare Biologie der Universitaet Heidelberg, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
Journal of Unsolved Questions, 2, 1, Articles 1-4, 2012 (Received October 17th, accepted November 30th, published December 3rd 2011)
The protein CheB is an integral component of sensory adaptation in the chemotaxis system of Escherichia coli. It catalyzes demethylation of the chemoreceptors thereby opposing the effect of ligands on kinase activity. The kinase enhances the activity of the methylesterase via phosphotransfer, thus creating a negative feedback. Although CheB phosphorylation depends on the receptor state, it is not essential for precise adaptation. Therefore, the feedback mechanism is proposed through modeling to compensate for protein fluctuations in the chemotaxis network.
Swarm plate assays revealed that chemotaxis performance in general was even more robust against deviations of single protein concentrations than predicted. However, phosphorylation deficient mutants of CheB still enabled an appropriate chemotaxis response as compared to wild type CheB. Furthermore, when simulations were recoded to include CheB phosphorylation, there was no effect on swarming. Hence both, measured and calculated swarm efficiencies indicate that CheB phosphorylation does not improve robustness of chemotaxis against perturbations in protein levels.
Keywords: Bacteria, Chemotaxis, Feedback, Robustness