Similar molecular strategies are used in stimulus/response coupling in all cells. The process generally involves transmembrane receptors located at the cell surface and a set of intracellular signal transduction proteins that carry information from the receptors to the target proteins that mediate the specific responses. Bacterial chemotaxis is an ideal model system for investigating the molecular mechanism of receptor-mediated signal transduction. The system is composed of a small number of components; a family of transmembrane receptor proteins, two receptor modifying enzymes, the flagellar motor apparatus, and four cytoplasmic signal transduction proteins that process information linking receptor signaling to the motor response. The central signal transduction mechanism in chemotaxis involves phosphotransfer from a histidine protein kinase, CheA, to a phosphorylation-activated regulator protein that controls the direction of flagellar rotation, CheY. Autophosphorylation of the kinase, CheA, is regulated by the receptors in a mechanism that requires the auxiliary protein, CheW, and is dependent on both the degree of receptor ligand occupancy, and on the modification state of the receptor. The system provides an opportunity for elucidating the fundamental principles of protein modification reactions and protein/protein interactions in regulatory biochemistry. %%% A molecular description of signal transduction in the model system of bacterial chemotaxis is critical to understanding the fundamental chemical strategies for complex regulatory phenomena such as signal amplification and adaptation. Dr. Stock's laboratory is using a combination of molecular genetic, biochemical, and biophysical methods to correlate structure and function of several signal transduction proteins.
