Negatively charged phospholipids influence the activity of the sensor kinase KdpD of Escherichia coli.

Synthesis of the high-affinity K(+)-translocating Kdp-ATPase of Escherichia coli, encoded by the kdpFABC operon, is regulated by the membrane-bound sensor kinase KdpD and the soluble response regulator KdpE. K(+) limitation or a sudden increase in osmolarity induces the expression of kdpFABC. Due to the importance of K(+) to maintain turgor, it has been proposed that KdpD is a turgor sensor. Although the primary stimulus that KdpD senses is unknown, alterations in membrane strain or the interaction between KdpD and membrane components might be good candidates. Here, we report a study of the influence of the membrane phospholipid composition on the function of KdpD in vivo and in vitro using various E. coli mutants defective in phospholipid biosynthesis. Surprisingly, neither the lack of the major E. coli phospholipid phosphatidylethanolamine nor the drastic reduction of the phosphatidylglycerol/cardiolipin content influenced induction of kdpFABC expression significantly. However, in vitro reconstitution experiments with synthetic phospholipids clearly demonstrated that KdpD kinase activity is dependent on negatively charged phospholipids, whereas the structure of the phospholipids plays a minor role. These results indicate that electrostatic interactions are important for the activity of KdpD.