Chemotactic bacteria utilize a highly sensitive and adaptable sensory system to swim towards attractants and away from repellents. A polar, highly organized sensory patch of transmembrane receptor proteins detects changes in nutrient concentrations. Attractants and repellents bind to the sensory domains of these receptors, thereby regulating the activity of the histidine kinase CheA, which phosphorylates a soluble messenger protein. This messenger protein then diffuses through the cytoplasm to the flagellar basal body, where it modulates the direction of flagellar rotation. Besides the membrane-bound chemoreceptor arrays, many motile bacteria contain one or more additional, purely cytoplasmic chemoreceptor systems that are required for a chemotactic response in these organisms.
I will present new insights into the assembly process and the detailed arrangement of the chemotaxis proteins in these massive macromolecular complexes, which has given us a new understanding about structural changes in the array that occur upon activation.