Analysis of KdpC of the K+-transporting KdpFABC complex of Escherichia coli

The Kdp complex, a high affinity ATP-driven K+ transport system of Escheric hia coli, is composed of the four membrane-bound subunits KdpF, KdpA, KdpB and KdpC. Whereas the role of KdpB (catalytical subunit), KdpA (K+-transloc ating subunit) and KdpF (stabilizing peptide) is well understood, the funct ion of KdpC is still unknown. Therefore, a kdpC deletion strain was constru cted and complementation experiments were performed using different kdpC co nstructs. Truncations of the kdpC gene revealed that only one derivative, w hich lacks base pairs coding for the four C-terminal amino acids, was able to complement the chromosomal deletion of kdpC. Furthermore, complementatio n was also observed with kdpC of Mycobacterium tuberculosis, but not with k dpC from Clostridium acetobutylicum or Synechocystis sp. PCC6803. Sequence alignment of 17 different KdpC proteins led to the construction of hybrids between kdpC of E. coli and that of C. acetobutylicum. Complementation reve aled that the N-terminal transmembrane segment as well as the C-terminal-th ird of the protein can be exchanged between both species, but only one afte r the other. A simultaneous substitution of both regions was not possible.