‘Fine tuned model for perfect adaptation’ Spiro et al. PNAS 94, 7263-7268 (1997) A model of excitation and adaptation in bacterial chemotaxis key player: Tar-CheA-CheW complex Copyright (1997) National Academy of Sciences, U. S. A. Figure 1 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8. "A model of excitation and adaptation in bacterial chemotaxis." assumptions: 1. Tar is only receptor type, CheW and CheA always bound to Tar 2. Methylation occurs in specific order 3. Consider only 3 highest methylation states 4. Only CheB p demethylates 5. Phoshorylation of CheA does not affect ligand (un)binding 6. Tar-CheR binding does not affect ligand un(binding) and phosphorylation of CheA 7. CheZ is not regulated 8. Phosphotransfer from complex to CheY or CheB is not affected by occupancy or methylation state. fast slow i n t e r m e d i a t e Copyright (1997) National Academy of Sciences, U. S. A. Figure 2 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8. "A model of excitation and adaptation in bacterial chemotaxis." Ligand bound states generally have lower autophosphoryalation rates Copyright (1997) National Academy of Sciences, U. S. A. Copyright (1997) National Academy of Sciences, U. S. A. Figure 2 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8. "A model of excitation and adaptation in bacterial chemotaxis." CheR methylates ligand-bound states more rapidly Copyright (1997) National Academy of Sciences, U. S. A. Figure 2 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8."A model of excitation and adaptation in bacterial chemotaxis." Consider step in aspartate concentration time ~ 1 ms, increase in ligand bound complex Copyright (1997) National Academy of Sciences, U. S. A. Figure 2 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8."A model of excitation and adaptation in bacterial chemotaxis." time ~ 5 s, total # of phosphorylated complexes decreases gradually because ligand bound complexes do not autophoshorylate very well also: CheB p decreases low CheA p , low CheY p , tumble suppression Copyright (1997) National Academy of Sciences, U. S. A. Figure 2 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. "A model of excitation and adaptation in bacterial chemotaxis." Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8. time ~ 50 s, slowly the complex methylates. Note that demethylation is switched off because of low levels of CheA p (low CheB p ). also low CheA p , low CheY p , tumble suppression Copyright (1997) National Academy of Sciences, U. S. A. Figure 4 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. "A model of excitation and adaptation in bacterial chemotaxis." Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8. Higher methylation states autophosphorylate easier, so slowly CheA p adapts to its initial level high CheA p , high CheY p , tumbling Copyright (1997) National Academy of Sciences, U. S. A. Figure 4 of Spiro, P. A., J. S. Parkinson, and H. G. Othmer. "A model of excitation and adaptation in bacterial chemotaxis." Proc Natl Acad Sci U S A 94, no. 14 (Jul 8, 1997): 7263-8. CheY p CheB p Copyright (1997) National Academy of Sciences, U. S. A. Spiro, P. A., J. S. Parkinson, and H. G. Othmer. Figures 1, 2, and 4 in " Proc Natl Acad Sci U S A 94, no. 14 (July 8, 1997): 7263-8. A model of excitation and adaptation in bacterial chemotaxis." Image removed due to copyright considerations. See Figures 2 and 3 in Barkai, N., S. Leibler. "Robustness in simple biochemical networks." Nature 387, no. 6636 (Jun 26, 1997): 913-7. Image removed due to copyright considerations. See Figures 2 and 3 in Barkai, N., S. Leibler. "Robustness in simple biochemical networks." Nature 387, no. 6636 (Jun 26, 1997): 913-7. Image removed due to copyright considerations. See Figures 2 and 3 in Barkai, N., S. Leibler. "Robustness in simple biochemical networks." Nature 387, no. 6636 (Jun 26, 1997): 913-7.