Sr. Durell et al., Does the KdpA subunit from the high affinity K+-translocating P-type KDP-ATPase have a structure similar to that of K+ channels?, BIOPHYS J, 78(1), 2000, pp. 188-199
Evidence is presented that the transmembrane KdpA subunit of the high affin
ity K+-translocating P-type Kdp-ATPase is evolutionarily derived from the s
uperfamily of 2TM-type K+ channels in bacteria. This extends a previous stu
dy relating the K+ channels to the KtrAB, Trk, Trk1,2, and HKT1 K+ symporte
r superfamily of both prokaryotes and eukaryotes, Although the channels are
formed by four single-MPM motif subunits, the transmembrane KdpA subunit a
nd the transmembrane subunit of the symporter proteins are postulated to ha
ve four corresponding MPM motifs within a single sequence. Analysis of 17 K
dpA sequences reveals a pattern of residue conservation similar to that of
the symporters and channels, and consistent with the crystal structure of t
he KcsA K+ channel. In addition, the most highly conserved residues between
the families, specifically the central glycines of the P2 segments, are th
ose previously identified as crucial for the property of K+-selectivity tha
t is common to each protein. This hypothesis is consistent with an experime
ntal study of mutations that alter K+ binding affinity of the Kdp transport
er. Although most of the results of a previous study of the transmembrane t
opology 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.