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Adapt locally and act globally: strategy to maintain high chemoreceptor sensitivity in complex environments.

Lan G, Schulmeister S, Sourjik V, Tu Y - Mol. Syst. Biol. (2011)

Bottom Line: Permanent methylation crosstalk occurs when the system fails to adapt accurately.This local adaptation mechanism enables cells to differentiate individual stimuli by encoding them into the methylation levels of corresponding types of chemoreceptors.It tunes each receptor to its most responsive state to maintain high sensitivity in complex environments and prevents saturation of the cluster by one signal.

View Article: PubMed Central - PubMed

Affiliation: IBM T.J. Watson Research Center, Yorktown Heights, New York, NY, USA.

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Response sensitivity in different backgrounds and comparison with experiments. (A) The response sensitivities to MeAsp as functions of the background MeAsp level. Different panels are for different serine backgrounds. (B) The response sensitivities to serine as functions of the background serine level. Different panels are for different MeAsp backgrounds. (C, D) Show the dose–response curves for the LA (black) and GA (red) models at three different backgrounds shown by the dotted lines. The responses in three backgrounds ([L]0=30, 500 and 5000 μM MeAsp) are compared with the corresponding experimental measurements (Sourjik and Berg, 2002; diamond symbols) in (C). For comparison purpose, we subtracted background activity at saturate amount of MeAsp (C) or serine (D) and scaled the experimentally measured adapted activities to a0 in our model. The LA model shows excellent agreement with the experiments. Note that instead of plotting the response to the added concentration Δ[L] as done in Sourjik and Berg (2002), we have plotted the response against the final concentration [L]1=[L]0+Δ[L] so that the sensitivity can be directly determined from the slope of the response curve at [L]1=[L]0 (Mello and Tu, 2007). The results here indicate that for any given backgrounds, the LA model always leads to higher sensitivity than the GA model.
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f7: Response sensitivity in different backgrounds and comparison with experiments. (A) The response sensitivities to MeAsp as functions of the background MeAsp level. Different panels are for different serine backgrounds. (B) The response sensitivities to serine as functions of the background serine level. Different panels are for different MeAsp backgrounds. (C, D) Show the dose–response curves for the LA (black) and GA (red) models at three different backgrounds shown by the dotted lines. The responses in three backgrounds ([L]0=30, 500 and 5000 μM MeAsp) are compared with the corresponding experimental measurements (Sourjik and Berg, 2002; diamond symbols) in (C). For comparison purpose, we subtracted background activity at saturate amount of MeAsp (C) or serine (D) and scaled the experimentally measured adapted activities to a0 in our model. The LA model shows excellent agreement with the experiments. Note that instead of plotting the response to the added concentration Δ[L] as done in Sourjik and Berg (2002), we have plotted the response against the final concentration [L]1=[L]0+Δ[L] so that the sensitivity can be directly determined from the slope of the response curve at [L]1=[L]0 (Mello and Tu, 2007). The results here indicate that for any given backgrounds, the LA model always leads to higher sensitivity than the GA model.

Mentions: The most important performance measure of a sensory system is its sensitivity to various external stimuli in different backgrounds. For E. coli chemotaxis, after the mixed receptor cluster reaches its steady state in a given ambient chemical background, the response to a sudden change of a stimulus concentration (Δ[L]) can be measured by the relative sensitivity: S≡([Δ]〈a〉/〈a〉/Δ[L]/[L]), where Δa is the immediate activity change before methylation/demethylation takes place and [L] is the ambient level of the ligand whose concentration has been changed. Here, we compare the sensitivities of the Ising-type GA and the LA models in different backgrounds of MeAsp and serine concentrations. In Figure 7A, we plot the sensitivity to MeAsp as a function of the background MeAsp concentration at different levels of serine background. Results show that higher levels of serine background do not change the shape of the sensitivity curve, but lower the overall sensitivity to MeAsp, likely caused by the cell's imperfect adaptation to serine. The serine sensitivity curves in different levels of MeAsp backgrounds, as shown in Figure 7B, have little or no dependence on the MeAsp backgrounds, as the cell can adapt to a wide range of MeAsp concentrations accurately. More systematic evaluations have been performed under all combinations of background MeAsp and serine concentrations, and the results are summarized in Supplementary Figure S7. For responses to all combinations of MeAsp and serine, the LA scheme for the Ising-type model always leads to a higher sensitivity than the global scheme (see also Supplementary Figure S7).


Adapt locally and act globally: strategy to maintain high chemoreceptor sensitivity in complex environments.

Lan G, Schulmeister S, Sourjik V, Tu Y - Mol. Syst. Biol. (2011)

Response sensitivity in different backgrounds and comparison with experiments. (A) The response sensitivities to MeAsp as functions of the background MeAsp level. Different panels are for different serine backgrounds. (B) The response sensitivities to serine as functions of the background serine level. Different panels are for different MeAsp backgrounds. (C, D) Show the dose–response curves for the LA (black) and GA (red) models at three different backgrounds shown by the dotted lines. The responses in three backgrounds ([L]0=30, 500 and 5000 μM MeAsp) are compared with the corresponding experimental measurements (Sourjik and Berg, 2002; diamond symbols) in (C). For comparison purpose, we subtracted background activity at saturate amount of MeAsp (C) or serine (D) and scaled the experimentally measured adapted activities to a0 in our model. The LA model shows excellent agreement with the experiments. Note that instead of plotting the response to the added concentration Δ[L] as done in Sourjik and Berg (2002), we have plotted the response against the final concentration [L]1=[L]0+Δ[L] so that the sensitivity can be directly determined from the slope of the response curve at [L]1=[L]0 (Mello and Tu, 2007). The results here indicate that for any given backgrounds, the LA model always leads to higher sensitivity than the GA model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3094069&req=5

f7: Response sensitivity in different backgrounds and comparison with experiments. (A) The response sensitivities to MeAsp as functions of the background MeAsp level. Different panels are for different serine backgrounds. (B) The response sensitivities to serine as functions of the background serine level. Different panels are for different MeAsp backgrounds. (C, D) Show the dose–response curves for the LA (black) and GA (red) models at three different backgrounds shown by the dotted lines. The responses in three backgrounds ([L]0=30, 500 and 5000 μM MeAsp) are compared with the corresponding experimental measurements (Sourjik and Berg, 2002; diamond symbols) in (C). For comparison purpose, we subtracted background activity at saturate amount of MeAsp (C) or serine (D) and scaled the experimentally measured adapted activities to a0 in our model. The LA model shows excellent agreement with the experiments. Note that instead of plotting the response to the added concentration Δ[L] as done in Sourjik and Berg (2002), we have plotted the response against the final concentration [L]1=[L]0+Δ[L] so that the sensitivity can be directly determined from the slope of the response curve at [L]1=[L]0 (Mello and Tu, 2007). The results here indicate that for any given backgrounds, the LA model always leads to higher sensitivity than the GA model.
Mentions: The most important performance measure of a sensory system is its sensitivity to various external stimuli in different backgrounds. For E. coli chemotaxis, after the mixed receptor cluster reaches its steady state in a given ambient chemical background, the response to a sudden change of a stimulus concentration (Δ[L]) can be measured by the relative sensitivity: S≡([Δ]〈a〉/〈a〉/Δ[L]/[L]), where Δa is the immediate activity change before methylation/demethylation takes place and [L] is the ambient level of the ligand whose concentration has been changed. Here, we compare the sensitivities of the Ising-type GA and the LA models in different backgrounds of MeAsp and serine concentrations. In Figure 7A, we plot the sensitivity to MeAsp as a function of the background MeAsp concentration at different levels of serine background. Results show that higher levels of serine background do not change the shape of the sensitivity curve, but lower the overall sensitivity to MeAsp, likely caused by the cell's imperfect adaptation to serine. The serine sensitivity curves in different levels of MeAsp backgrounds, as shown in Figure 7B, have little or no dependence on the MeAsp backgrounds, as the cell can adapt to a wide range of MeAsp concentrations accurately. More systematic evaluations have been performed under all combinations of background MeAsp and serine concentrations, and the results are summarized in Supplementary Figure S7. For responses to all combinations of MeAsp and serine, the LA scheme for the Ising-type model always leads to a higher sensitivity than the global scheme (see also Supplementary Figure S7).

Bottom Line: Permanent methylation crosstalk occurs when the system fails to adapt accurately.This local adaptation mechanism enables cells to differentiate individual stimuli by encoding them into the methylation levels of corresponding types of chemoreceptors.It tunes each receptor to its most responsive state to maintain high sensitivity in complex environments and prevents saturation of the cluster by one signal.

View Article: PubMed Central - PubMed

Affiliation: IBM T.J. Watson Research Center, Yorktown Heights, New York, NY, USA.

Show MeSH
Related in: MedlinePlus