Speaker:  Prof. N Wingreen, Dept. of Molecular Biology, Princeton University

Title: Chemosensing in E. coli: Two regimes of two-state receptors

Abstract: E. coli chemotax by detecting temporal changes in their chemical environment and transducing this information into a decision to swim straight or change direction (tumble). The chemotaxis network in E. coli is remarkable for its sensitivity to small relative changes in the concentrations of multiple chemical signals. We present a model for signal integration by mixed clusters of interacting two-state chemoreceptors. Our model results compare favorably to the results obtained by Sourjik and Berg using in vivo fluorescence resonance energy transfer (FRET), both for wild-type and non-adapting mutant strains. Importantly, we identify two distinct regimes of behavior, depending on the relative energies of the two states of the receptors. In regime I, coupling of receptors leads to high sensitivity, while in regime II, coupling of receptors leads to high cooperativity, i.e. high Hill coefficient. For homogeneous receptor clusters, we predict an observable transition between regime I and regime II with increasing receptor methylation or amidation.

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