STRUCTURAL AND BIOCHEMICAL STUDIES OF BACTERIAL

Transmembrane chemoreceptors, also known as methyl-accepting chemotaxis proteins (MCPs), translate extracellular signals into intracellular responses in the bacterial chemotaxis system. MCPs control the activity of the kinase, CheA, via a coupling protein, CheW. The chemoreceptor, CheA and CheW form a ternary complex that is the central signaling unit in bacterial chemotaxis. Although the individual structures of the components of the ternary complex are known, the precise molecular associations of these proteins has yet to be identified. Here we present a soluble stable ternary complex from Thermotoga maritima that can be used to probe the molecular interactions between MCP, CheA and CheW. The stoichiometry of this soluble complex was determined to be one MCP dimer: one CheA dimer: two CheW dimers. In this complex the autophosphorylating activity of CheA was significantly inhibited by the soluble MCP, Tm14. The cytoplasmic portion of a T. maritima transmembrane MCP (Tm1143) also inhibited the activity of CheA to varying degrees depending on specific mutations that mimi