Structural analysis of bacterial chemotaxis proteins: Components of a dynamic signaling system

Most motile bacteria are capable of directing their movement in response to chemical gradients, a behavior known as chemotaxis. The signal transductio n system that mediates chemotaxis in enteric bacteria consists of a set of six cytoplasmic proteins that couple stimuli sensed by a family of transmem brane receptors to behavioral responses generated by the flagellar motors. Signal transduction occurs via a phosphotransfer pathway involving a histid ine protein kinase, CheA, and a response regulator protein, CheY, that in i ts phosphorylated state, modulates the direction of flagellar rotation. Two auxiliary proteins, CheW and CheZ, and two receptor modification enzymes, methylesterase CheB and methyltransferase CheR, influence the flux of phosp horyl groups within this central pathway. This paper focuses on structural characteristics of the four signaling proteins (CheA, CheY, CheB, and CheR) for which MMR or x-ray crystal structures have been determined. The protei ns are examined with respect to their signaling activities that involve rev ersible protein modifications and transient assembly of macromolecular comp lexes. A variety of data suggest conformational flexibility of these protei ns, a feature consistent with their multiple roles in a dynamic signaling p athway. (C) 1998 Academic Press.