Data obtained early on suggested that the chemotactic response is proportional to the change in receptor occupancy, with that occupancy characterized by a fixed dissociation constant, K d, the concentration of ligand at which the probability of receptor occupancy is 1/2 (Berg and Tedesco, 1975; Mesibov et al., 1973). Then it became evident that the dissociation constant increases (i.e., cells become less sensitive) at higher concentrations of ligand, as receptors are methylated (Borkovich et al., 1992; Bornhorst and Falke, 2000; Dunten and Koshland 1991; Li and Weis, 2000). However, even at these higher concentrations (e.g., for the nonmetabolizable aspartate analog α-methylaspartate at an ambient concentration of 0.16 mM) the gain is prodigious: a step increase in concentration from 0.16 to 0.16 + 0.0027 mM (a change of about 1.7%) transiently increases the probability that the motor spins counterclockwise (CCW) by 0.23 (Segall et al., 1986). Computer simulations of the chemotaxis system (e.g., Bray et al., 1993; reviewed by Bray, 2002) fail to predict the necessary gain. Two recent findings appear to resolve the paradox. First, there is an amplification step at the beginning of the signaling pathway: the fractional change in kinase activity is some 35 times larger than the fractional change in receptor occupancy (Sourjik and Berg, 2002a).
KeywordsReceptor Occupancy Ambient Concentration Fractional Change Chemotactic Response Receptor Cluster
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Alon, U., M. G. Surette, N. Barkai, and S. Leibler. 1999. Robustness in bacterial chemotaxis. Nature
Ames, P., C. A. Studdert, R. H. Reiser, and J. S. Parkinson. 2002. Collaborative signaling by mixed chemoreceptor teams in Escherichia coli
. Proc. Natl. Acad. Sci. USA
Barkai, N., and S. Leibler. 1997. Robustness in simple biochemical networks. Nature
Berg, H. C., and E. M. Purcell. 1977. Physics of chemoreception. Biophys. J.
Berg, H. C., and P. M. Tedesco. 1975. Transient response to chemotactic stimuli in Escherichia coli
. Proc. Natl. Acad. Sci. USA
Berg, H. C., and L. Turner. 1995. Cells of Escherichia coli
swim either end forward. Proc. Natl. Acad. Sci. USA
Borkovich, K. A., L. A. Alex, and M. I. Simon. 1992. Attenuation of sensory receptor signaling by covalent modification. Proc. Natl. Acad. Sci. USA
Bornhorst, J. A., and J. J. Falke. 2000. Attractant regulation of the aspartate receptor-kinase complex: limited cooperative interactions between receptors and effects of the receptor modification state. Biochemistry
Bray, D. 2002. Bacterial chemotaxis and the question of gain. Proc. Natl. Acad. Sci. USA
Bray, D., R. B. Bourret, and M. I. Simon. 1993. Computer simulation of the phosphorylation cascade controlling bacterial chemotaxis. Mol. Biol. Cell
Cluzel, P., M. Surette, and S. Leibler. 2000. An ultrasensitive bacterial motor revealed by monitoring signaling proteins in single cells. Science
Duke, T. A. J., and D. Bray. 1999. Heightened sensitivity of a lattice of membrane receptors. Proc. Natl. Acad. Sci. USA
Duke, T. A. J., N. Le Novère, and D. Bray. 2001. Conformational spread in a ring of proteins: a stochastic approach to allostery. J. Mol. Biol.
Dunten, P., and D. E. Koshland, Jr. 1991. Tuning the responsiveness of a sensory receptor via covalent modification. J. Biol. Chem.
266: 1491–1496.Google Scholar
Falke, J. L. 2002. Cooperactivity between bacterial chemotaxis receptors. Proc. Natl. Acad. Sci. USA
Gestwicki, J. E., and L. L. Kiessling. 2002. Inter-receptor communication through arrays of bacterial chemoreceptors. Nature
Li, G., and R. M. Weis. 2000. Covalent modification regulates ligand binding to receptor complexes in the chemosensory system of Escherichia coli
Maddock, J. R., and L. Shapiro. 1993. Polar location of the chemoreceptor complex in the Escherichia coli
Mesibov, R., G. W. Ordal, and J. Adler. 1973. The range of attractant concentrations for bacterial chemotaxis and the threshold and size of response over this range. J. Gen. Physiol.
Monod, J., J. Wyman, and J.-P. Changeux. 1965. On the nature of allosteric transitions: a plausible model. J. Mol. Biol.
Segall, J. E., S. M. Block, and H. C. Berg. 1986. Temporal comparisons in bacterial chemotaxis. Proc. Natl. Acad. Sci. USA
Shimizu, T. S., N. Le Novère, M. D. Levin, A. J. Beavil, B. J. Sutton, and D. Bray. 2000. Molecular model of a lattice of signalling proteins involved in bacterial chemotaxis. Nature Cell Biol.
Sourjik, V., and H. C. Berg. 2000. Localization of components of the chemotaxis machinery of Escherichia coli
using fluorescent protein fusions. Mol. Microbiol.
Sourjik, V., and H. C. Berg. 2002a. Receptor sensitivity in bacterial chemotaxis. Proc. Natl. Acad. Sci. USA
Sourjik, V., and H. C. Berg. 2002b. Binding of the Escherichia coli
response regulator CheY to its target measured in vivo by fluorescence resonance energy transfer. Proc. Natl. Acad. Sci. USA
© Springer-Verlag New York, Inc. 2004