Biophys J, January 2000, p. 188-199, Vol. 78, No. 1

Does the KdpA Subunit from the High Affinity K⁺-Translocating P-Type KDP-ATPase have a Structure Similar to That of K⁺ Channels?

Stewart R. Durell,^* Evert P. Bakker, and H. Robert Guy^*

 ^*Laboratory of Experimental and Computational Biology, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bethesda, Maryland 20892-5677, USA, and  Abteilung Mikrobiologie, Universität Osnabrück, D-49069 Osnabrück, Germany

Evidence is presented that the transmembrane KdpA subunit of the high affinity K⁺-translocating P-type Kdp-ATPase is evolutionarily derived from the superfamily of 2TM-type K⁺ channels in bacteria. This extends a previous study relating the K⁺ channels to the KtrAB, Trk, Trk1,2, and HKT1 K⁺ symporter superfamily of both prokaryotes and eukaryotes. Although the channels are formed by four single-MPM motif subunits, the transmembrane KdpA subunit and the transmembrane subunit of the symporter proteins are postulated to have four corresponding MPM motifs within a single sequence. Analysis of 17 KdpA sequences reveals a pattern of residue conservation similar to that of the symporters and channels, and consistent with the crystal structure of the KcsA K⁺ channel. In addition, the most highly conserved residues between the families, specifically the central glycines of the P2 segments, are those previously identified as crucial for the property of K⁺-selectivity that is common to each protein. This hypothesis is consistent with an experimental study of mutations that alter K⁺ binding affinity of the Kdp transporter. Although most of the results of a previous study of the transmembrane topology of KdpA are consistent with the 4-MPM model, the one deviation can be explained by a plausible change in the structure due to the experimental method.

Biophys J, January 2000, p. 188-199, Vol. 78, No. 1
© 2000 by the Biophysical Society   0006-3495/00/01/188/12  $2.00

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