Kinetic study of histidine kinase CheA in bacterial chemotaxis
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Histidine kinase CheA is central to signaling in bacterial chemotaxis. This kinase is responsible for the phosphorylation of two response regulators, CheY and CheB. CheY controls flagellar rotation and thus motility. CheB is crucial for sensory adaptation. CheA is dramatically activated, up to 1000-fold, and put under the control of chemoreceptors by formation of the signaling complex. As measured by phosphorylation of CheY, this control modulates the activity of CheA in a range as wide as two orders of magnitude. This change in the activity of CheA is the essence of chemotactic signaling. However, the enzymatic properties altered by kinase incorporation into signaling complexes, chemoreceptor ligand binding or receptor adaptational modification are largely undefined. This dissertation describes the kinetic analysis of kinase CheA. Data are fit to the Michaelis-Menten equation, from which important parameters KM and kcat are obtained. Based on these parameters for CheA at different signaling conditions, important observations and conclusions are made to contribute to better understanding of the control of the activity of kinase CheA, thus the bacterial chemotaxis signaling system.