Structural and chemical requirements for histidine phosphorylation by the chemotaxis kinase CheA |
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Authors: | Quezada Cindy M Hamel Damon J Gradinaru Cristian Bilwes Alexandrine M Dahlquist Frederick W Crane Brian R Simon Melvin I |
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Institution: | Division of Biology, California Institute of Technology, Pasadena, California 91125, USA. |
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Abstract: | The CheA histidine kinase initiates the signal transduction pathway of bacterial chemotaxis by autophosphorylating a conserved histidine on its phosphotransferase domain (P1). Site-directed mutations of neighboring conserved P1 residues (Glu-67, Lys-48, and His-64) show that a hydrogen-bonding network controls the reactivity of the phospho-accepting His (His-45) in Thermotoga maritima CheA. In particular, the conservative mutation E67Q dramatically reduces phosphotransfer to P1 without significantly affecting the affinity of P1 for the CheA ATP-binding domain. High resolution crystallographic studies revealed that although all mutants disrupt the hydrogen-bonding network to varying degrees, none affect the conformation of His-45. 15N-NMR chemical shift studies instead showed that Glu-67 functions to stabilize the unfavored N(delta1)H tautomer of His-45, thereby rendering the N(epsilon2) imidazole unprotonated and well positioned for accepting the ATP phosphoryl group. |
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