Two-state model for bacterial chemoreceptor proteins The role of multiple methylation Export

@article{1984Asakura, abstract = {To help understand the bacterial chemotactic response of excitation and adaptation, we propose a simple two-state model for receptor proteins (methyl-accepting chemotaxis proteins), in the light of evidence that they undergo multiple methylation in a preferred order. The model includes the following assumptions. (1) The receptor protein is in rapid equilibrium between two conformations, S and T, and the equilibrium shifts towards the T form as the number of methyl groups increases. (2) Attractants bind to the S form of the receptor, repellents bind to the T form, and both classes of ligand shift the S/T equilibrium according to the mass-action law. (3) The S form of the receptor accepts methyl groups one by one in a definite order, while the T form releases the methyl groups in the reverse order. Methylation and demethylation are slow reactions, and changes in the total number of methyl groups lag behind shifts in the S/T equilibrium. (4) The pattern of bacterial swimming at any moment is determined by the partition of the receptor between the two conformations, with tumbling frequency being a monotonically increasing function of the total T fraction of the receptor. This model shows that, if the receptor satisfies two sets of relationships imposed on its equilibrium and kinetic constants, it can maintain the steady-state total T fraction essentially constant over a broad range of ligand concentration, enabling cells to adapt to large changes in chemical environment. A stepwise change in ligand concentration leads to a rapid change in the total T fraction (excitation), followed by a slow relaxation process (adaptation). Computer simulations have been made of the whole response process, employing a receptor with six methylation sites per molecule and assuming simple sets of parameters. The results are in general agreement with published data on receptor methylation, as well as with a variety of observations of bacterial chemoresponse. Multiple methylation of the receptor proves to be necessary for the cells to respond sensitively to environmental changes.}, author = {Asakura, S.}, citeulike-article-id = {4749960}, citeulike-linkout-0 = {http://dx.doi.org/10.1016/0022-2836(84)90494-7}, citeulike-linkout-1 = {http://linkinghub.elsevier.com/retrieve/pii/0022-2836(84)90494-7}, doi = {10.1016/0022-2836(84)90494-7}, issn = {00222836}, journal = {Journal of Molecular Biology}, keywords = {adaptation, chemotaxis, four-state, model}, month = {July}, number = {3}, pages = {349--367}, posted-at = {2009-06-05 11:16:11}, priority = {2}, title = {Two-state model for bacterial chemoreceptor proteins The role of multiple methylation}, url = {http://dx.doi.org/10.1016/0022-2836(84)90494-7}, volume = {176}, year = {1984} }

TY - JOUR ID - 1984Asakura L3 - citeulike-article-id:4749960 N2 - To help understand the bacterial chemotactic response of excitation and adaptation, we propose a simple two-state model for receptor proteins (methyl-accepting chemotaxis proteins), in the light of evidence that they undergo multiple methylation in a preferred order. The model includes the following assumptions. (1) The receptor protein is in rapid equilibrium between two conformations, S and T, and the equilibrium shifts towards the T form as the number of methyl groups increases. (2) Attractants bind to the S form of the receptor, repellents bind to the T form, and both classes of ligand shift the S/T equilibrium according to the mass-action law. (3) The S form of the receptor accepts methyl groups one by one in a definite order, while the T form releases the methyl groups in the reverse order. Methylation and demethylation are slow reactions, and changes in the total number of methyl groups lag behind shifts in the S/T equilibrium. (4) The pattern of bacterial swimming at any moment is determined by the partition of the receptor between the two conformations, with tumbling frequency being a monotonically increasing function of the total T fraction of the receptor. This model shows that, if the receptor satisfies two sets of relationships imposed on its equilibrium and kinetic constants, it can maintain the steady-state total T fraction essentially constant over a broad range of ligand concentration, enabling cells to adapt to large changes in chemical environment. A stepwise change in ligand concentration leads to a rapid change in the total T fraction (excitation), followed by a slow relaxation process (adaptation). Computer simulations have been made of the whole response process, employing a receptor with six methylation sites per molecule and assuming simple sets of parameters. The results are in general agreement with published data on receptor methylation, as well as with a variety of observations of bacterial chemoresponse. Multiple methylation of the receptor proves to be necessary for the cells to respond sensitively to environmental changes. IS - 3 JF - Journal of Molecular Biology SN - 00222836 EP - 367 TI - Two-state model for bacterial chemoreceptor proteins The role of multiple methylation VL - 176 SP - 349 KW - adaptation KW - chemotaxis KW - four-state KW - model AU - Asakura, S PY - 1984/07// UR - http://dx.doi.org/10.1016/0022-2836(84)90494-7 ER -