STIMULUS-RESPONSE COUPLING IN BACTERIAL CHEMOTAXIS - RECEPTOR DIMERS IN SIGNALING ARRAYS

In the Escherichia coli chemotaxis system, a family of chemoreceptors in the cytoplasmic membrane binds stimulatory ligands and regulates th e activity of an associated histidine kinase CheA to modulate swimming behaviour and thereby cause a net migration towards attractants and a way from repellents. The chemoreceptors themselves have been shown to be predominantly dimeric, but in the presence of the kinase CheA plus an adapter protein, CheW, much higher order structures have been obser ved. Recent results indicate that transmembrane signalling occurs with in receptor clusters rather than through isolated dimers. We propose t hat the mechanism involves receptor arrays where binding of ligands at the outside surface of the membrane affects lateral packing interacti ons that cause perturbations in the organization of the signalling arr ay at the opposing surface of the membrane. Results with receptor chim eras as well as findings with tyrosine kinase receptors suggest that t his mechanism may represent a common theme in membrane receptor functi on.