The KdpF subunit is part of the K+-translocating Kdp complex of Escherichia coli and is responsible for stabilization of the complex in vitro

The hdpABC operon codes for the high affinity K+-translocating Kdp complex (P-type ATPase) of Escherichia coil, Upon expression of this operon in mini cells, a so far unrecognized small hydrophobic polypeptide, KdpF, could be identified on high resolution SDS-polyacrylamide gels in addition to the su bunits KdpA, KdpB, and KdpC, Furthermore, it could be demonstrated that Kdp F remains associated with the purified complex. As determined by mass spect rometry, this peptide is present in its formylated form and has a molecular mass of 3100 Da, KdpF is not essential for growth on low K+ (0.1 mM) mediu m, as shown by deletion analysis of KdpF, but proved to be indispensable fo r a functional enzyme complex in vitro. In the absence of KdpF, the ATPase activity of the membrane-bound Hdp complex was almost indistinguishable fro m that of the wild type. In contrast, the purified detergent-solubilized en zyme complex showed a dramatic decrease in enzymatic activity. However, add ition of purified KdpF to the KdpABC complex restored the activity up to wi ld type level, It is interesting to note that the addition of high amounts of E. coil lipids had a similar effect. Although KdpF is not essential for the function of the Hdp complex in vivo, it is part of the complex and func tions as a stabilizing element in vitro, The corresponding operon should no w be referred to as kdpFABC.