ASSEMBLY AND FUNCTION OF A QUATERNARY SIGNAL-TRANSDUCTION COMPLEX MONITORED BY SURFACE-PLASMON RESONANCE

WE have used surface plasmon resonance biosensor technology to monitor the assembly and dynamics of a signal transduction complex which cont rols chemotaxis in Escherichia coli. A quaternary complex formed which consisted of the response regulator CheY, the histidine protein kinas e CheA, a coupling protein CheW and a membrane-bound chemoreceptor Tar . Using various experimental conditions and mutant proteins, we have s hown that the complex dissociates under conditions that favour phospho rylation of CheY. Direct physical analysis of interactions among prote ins in this signal transduction pathway provides evidence for a previo usly unrecognized binding interaction between the kinase and its subst rate. This interaction may be important for enhancing substrate specif icity and preventing 'crosstalk' with other systems. The approach is g enerally applicable to furthering our understanding of how signalling complexes transduce intracellular messages.