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Abstract: The basic structural unit of the signaling complex in bacterial chemotaxis consists of the chemotaxis kinase CheA, the coupling protein CheW, and chemoreceptors. These complexes play an important role in regulating the kinase activity of CheA and in turn controlling the rotational bias of the flagellar motor. Although individual three-dimensional structures of CheA, CheW, and chemoreceptors have been determined, the interaction between chemoreceptor and CheW is still unclear. We used nuclear magnetic resonance to characterize the interaction modes of chemoreceptor and CheW from Thermotoga maritima. We find that chemoreceptor binding surface is located near the highly conserved tip region of the N-terminal helix of the receptor, whereas the binding interface of CheW is placed between the β-strand 8 of domain 1 and the β-strands 1 and 3 of domain 2. The receptor–CheW complex shares a similar binding interface to that found in the “trimer-of-dimers” oligomer interface seen in the crystal structure of cytoplasmic domains of chemoreceptors from Escherichia coli. Based on the association constants inferred from fast exchange chemical shifts associated with receptor–CheW titrations, we estimate that CheW binds about four times tighter to its first binding site of the receptor dimer than to its second binding site. This apparent anticooperativity in binding may reflect the close proximity of the two CheW binding surfaces near the receptor tip or further, complicating the events at this highly conserved region of the receptor. This work describes the first direct observation of the interaction between chemoreceptor and CheW. [Copyright &y& Elsevier]

Abstract: The bacterial chemotaxis adaptor protein CheW physically links the chemoreceptors (MCPs) and the histidine kinase CheA. Extensive investigations using bacterium Escherichia coli have established the central role of CheW in the MCP-modulated activation of CheA. Here we report the solution structure of CheW from E. coli determined by NMR spectroscopy. The results show that E. coli CheW shares an overall fold with previously reported structure of CheW from Thermotoga maritima, whereas local conformational deviations are observed. In particular, the C-terminal α-helix is considerably longer in E. coli CheW and appears to shrink the active binding pocket with CheA. Our study provides the structural basis for further investigations in E. coli chemotaxis. [Copyright &y& Elsevier]