title: Does the KdpA subunit from the high affinity K(+)-translocating P-type KDP-ATPase have a structure similar to that of K(+) channels?
abstract: 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.
authors.affiliation: Laboratory of Experimental Biology, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bethesda, Maryland 20892-5677, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Durell
authors.forename: E P
authors.initials: EP
authors.lastname: Bakker
authors.forename: H R
authors.initials: HR
authors.lastname: Guy
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000648:ultrastructure; D017124:Conserved Sequence; D019992:Databases as Topic; D029968:Escherichia coli Proteins; D019143:Evolution, Molecular; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019151:Peptide Library; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry*; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D019151:Peptide Library; D015221:Potassium Channels; D000251:Adenosine Triphosphatases; C058166:potassium translocating Kdp-ATPase, E coli; D011188:Potassium