Figure 15-66. The phosphorylation relay system that enables the chemotaxis receptors to control the flagellar motor.

Figure 15-66The phosphorylation relay system that enables the chemotaxis receptors to control the flagellar motor

The binding of a repellent increases the activity of the receptor, which binds CheW and CheA, thereby stimulating CheA to phosphorylate itself. CheA quickly transfers its covalently bound, high-energy phosphate directly to CheY to generate CheY-phosphate, which binds to the flagellar motor and causes it to rotate clockwise, resulting in tumbling. The binding of an attractant has the opposite effect. It decreases the activity of the receptor and therefore decreases the phosphorylation of CheA and CheY, which results in counterclockwise flagellar rotation and smooth swimming. CheZ accelerates the dephosphorylation of CheY-phosphate, thereby inactivating it. Each of the phosphorylated intermediates decays in about 10 seconds, enabling the bacterium to respond very quickly to changes in its environment (see Figure 15-10).

Image ch15f10

From: Target-Cell Adaptation

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 3rd edition.
Alberts B, Bray D, Lewis J, et al.
New York: Garland Science; 1994.
Copyright © 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D Watson.

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