Characterization of the KdpD protein, the sensor kinase of the K(+)-translocating Kdp system of Escherichia coli.

KdpD and KdpE, proteins that control expression of the kdpFABC operon, are members of the class of sensor kinase/response regulator proteins. Using polyclonal antibodies raised against the KdpD protein, we have been able to identify and to localize the chromosome-encoded KdpD protein in the cytoplasmic membrane of Escherichia coli. Furthermore, it has been possible to detect differences in the expression of the KdpD protein according to the K+ concentration in the growth medium.

KdpD and KdpE, proteins that control expression of the kdpABC operon, are members of the two-component sensor-effector class of regulators.

The Kdp system of Escherichia coli, a transport ATPase with high affinity for potassium, is expressed when turgor pressure is low. Expression requires KdpD, a 99-kDa membrane protein, and KdpE, a 25-kDa soluble cytoplasmic protein. The sequences of KdpD and KdpE show they are members of the sensor-effector class of regulatory proteins: the C-terminal half of KdpD is homologous to sensors such as EnvZ and PhoR, and KdpE is homologous to effectors such as OmpR and PhoB.