Covalent modification regulates ligand binding to receptor complexes in the chemosensory system of Escherichia coli

In the Escherichia coli chemosensory pathway, receptor modification mediate s adaptation to ligand. Evidence is presented that covalent modification in fluences ligand binding to receptors in complexes with CheW and the kinase CheA. Kinase inhibition was measured with serine receptor complexes in diff erent modification levels; K-i for serine-mediated inhibition increased 10, 000-fold from the lowest to the highest level. Without CheA and CheW, ligan d binding is unaffected by covalent modification; thus, the influence of co valent modification is mediated only in the receptor complex, a conclusion supported by an analogy to allosteric enzymes and the observation of cooper ative kinase inhibition. Also, the finding that a subsaturating serine conc entration accelerates active receptor-kinase complex assembly implies that the assembly/disassembly process may also contribute to kinase regulation.