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Chemotaxis in Escherichia coli: A Molecular Model for Robust Precise Adaptation

Department of Physics, Princeton University, Princeton, New Jersey, United States of America.
PLoS Computational Biology (Impact Factor: 4.83). 02/2008; 4(1):e1. DOI: 10.1371/journal.pcbi.0040001
Source: PubMed

ABSTRACT The chemotaxis system in the bacterium Escherichia coli is remarkably sensitive to small relative changes in the concentrations of multiple chemical signals over a broad range of ambient concentrations. Interactions among receptors are crucial to this sensitivity as is precise adaptation, the return of chemoreceptor activity to prestimulus levels in a constant chemoeffector environment. Precise adaptation relies on methylation and demethylation of chemoreceptors by the enzymes CheR and CheB, respectively. Experiments indicate that when transiently bound to one receptor, these enzymes act on small assistance neighborhoods (AN) of five to seven receptor homodimers. In this paper, we model a strongly coupled complex of receptors including dynamic CheR and CheB acting on ANs. The model yields sensitive response and precise adaptation over several orders of magnitude of attractant concentrations and accounts for different responses to aspartate and serine. Within the model, we explore how the precision of adaptation is limited by small AN size as well as by CheR and CheB kinetics (including dwell times, saturation, and kinetic differences among modification sites) and how these kinetics contribute to noise in complex activity. The robustness of our dynamic model for precise adaptation is demonstrated by randomly varying biochemical parameters.

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    • "It describes an organism's response to an external perturbation by returning state variables to their original values before perturbation. For example, perfect adaptation has been reported in bacterial (e.g., E. coli) chemotaxis (Berg and Tedesco, 1975; Alon et al., 1999; Yi et al., 2000; Hansen et al., 2008), osmotic-stress adaptations (Muzzey et al., 2009), and MAP-kinase regulation (Hao et al., 2007; Mettetal et al., 2008). Such perfect adaption behaviors are thought to be introduced through a time integral on the " controlled variable " in the network , which corresponds to a specific control system structure, i.e., an integral feedback control (Csete and Doyle, 2002). "
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    Frontiers in Microbiology 07/2014; 5:379. DOI:10.3389/fmicb.2014.00379 · 3.94 Impact Factor
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    • "A phosphatase, CheZ, dephosphorylates CheY-P. The chemotaxis pathway is well known for its high gain8,10–11, wide dynamic range11–12, and robust adaptation5,13, mediated by receptor methylation and demethylation (by CheR and CheB). "
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    • "Photoreceptors , as another example, respond to light intensities spanning 11 orders of magnitude [12]. The response to a broad dynamic range of input achieved by cellular signaling systems was often associated with their adaptive response, led by the intuition that the return of the system to its previous state allows renewed sensitivity to signal [13] [5] [10]. However, the quantitative relation between the two properties was not examined in detail. "
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