Assembly of the Kdp complex, the multi-subunit K+-transport ATPase of Escherichia coli

Kdp, the high affinity ATP-driven K+-transport system of Escherichia coli, is a complex of the membrane-bound subunits KdpA, KdpB, KdpC and the small peptide KdpF. The assembly of this complex was studied by the analysis of m utants that expressed two of the three large subunits and inserted them int o the cytoplasmic membrane. In the strains that do not express KdpC or KdpA the other two subunits did not copurify on dye-ligand affinity columns aft er solubilization with non-ionic detergent. In the mutant lacking KdpB the other two subunits copurified under the same conditions. It is concluded th at KdpC forms strong interactions with the KdpA subunit, serving to assembl e and stabilise the Kdp complex. A structure in which KdpC could be one of the connecting links between the energy-delivering subunit KdpB and the K+- transporting subunit KdpA is suggested by these data. (C) 1998 Elsevier Sci ence B.V. All rights reserved.