Cooperative model of bacterial sensing

Abstract

Bacterial chemotaxis is controlled by the signaling of a cluster of receptors. A cooperative model is presented, in which coupling between neighboring receptor dimers enhances the sensitivity with which stimuli can be detected, without diminishing the range of chemoeffector concentration over which chemotaxis can operate. Individual receptor dimers have two stable conformational states: one active, one inactive. Noise gives rise to a distribution between these states, with the probability influenced by ligand binding, and also by the conformational states of adjacent receptor dimers. The two-state model is solved, based on an equivalence with the Ising model in a randomly distributed magnetic field. The model has only two effective parameters, and unifies a number of experimental findings. According to the value of the parameter comparing coupling and noise, the signal can be arbitrarily sensitive to changes in the fraction of receptor dimers to which the ligand is bound. The counteracting effect of a change of methylation level is mapped to an induced field in the Ising model. By returning the activity to the prestimulus level, this adapts the receptor cluster to a new ambient concentration of chemoeffector, and ensures that a sensitive response can be maintained over a wide range of concentrations.

Quantitative modeling of sensitivity in bacterial chemotaxis: The role of coupling among different chemoreceptor species

“…Cooperativity between receptors as a mechanism for the system's large gain was first suggested by Bray, Levin, and MortonFirth (8). Later, Shi and Duke (9) proposed an Ising-type model, where identical receptors on a regular extended lattice interact with their nearest neighbors, as a materialization of the idea. Duke and Bray (10) eventually implemented a Monte Carlo version of the simple Ising-type model and demonstrated that it is capable of enhancing the gain of the system.…”

“…Each receptor, T qm , is characterized by three parameters: q is the type of receptor, only the two high-abundance types of receptors with q ϭ 1 for Tar and q ϭ 2 for Tsr being considered in this paper, and the total number of Tsr being twice that of Tar; m ʦ [0, 4] is the number of methyl groups; and ϭ 0, 1 represents vacant and ligand-occupied receptors, respectively. We assume the probability of finding the receptor in the active or inactive state is controlled by their energy difference and obeys the Boltzmann distribution (9). The average activity for receptor T qm is then given by:…”

From conformational spread to allosteric and cooperative models of E. coli flagellar motor

“…A sensing apparatus is devoted to detecting information about the environment, by measuring concentration of chemicals (generally called, in this context, chemoeffectors). The arrangement and functioning of the receptors present on E. coli cellular membrane has been extensively investigated also from the theoretical point of view (see, e.g., [4,5]). The information collected by the receptors is transduced to the flagellar motors through the "messenger molecule" CheY.…”

Clustering and signalling of cell receptors

“…Investigations on this issue are widely reported for various receptors, for example, integins, which attach cells to the extracellular matrix, tyrosine kinase receptors, cytoskine receptors, growth factor receptors, tumor necrosis factor receptors, including death receptors, antigen receptors such as T-cell receptors, bone morphogenetic protein receptor, G-protein-coupled receptors, etc [11][12][13][14][15][16][17][18][19]. In our previous works [2][3][4], the position of each receptor is fixed, and there is an a priori cluster. In the present article, we shall consider statistical mechanics of floating receptors.…”

“…In this case, thousands of receptors cluster together at a pole of the cell. Recently, based on detailed analyses on the experimental findings, I proposed that cooperative receptor-receptor interaction enhances the signalling, and constructed a statistical mechanical theory for this process [2][3][4]. My idea has since received considerable attention 1 .…”