title: The KdpC subunit of the Escherichia coli K+-transporting KdpB P-type ATPase acts as a catalytic chaperone.
abstract: In Bacteria and Archaea, high-affinity potassium uptake is mediated by the ATP-driven KdpFABC complex. On the basis of the biochemical properties of the ATP-hydrolyzing subunit KdpB, the transport complex is classified as type IA P-type ATPase. However, the KdpA subunit, which promotes K(+) transport, clearly resembles a potassium channel, such that the KdpFABC complex represents a chimera of ion pumps and ion channels. In the present study, we demonstrate that the blending of these two groups of transporters in KdpFABC also entails a nucleotide-binding mechanism in which the KdpC subunit acts as a catalytic chaperone. This mechanism is found neither in P-type ATPases nor in ion channels, although parallels are found in ABC transporters. In the latter, the ATP nucleotide is coordinated by the LSGGQ signature motif via double hydrogen bonds at a conserved glutamine residue, which is also present in KdpC. High-affinity nucleotide binding to the KdpFABC complex was dependent on the presence of this conserved glutamine residue in KdpC. In addition, both ATP binding to KdpC and ATP hydrolysis activity of KdpFABC were sensitive to the accessibility, presence or absence of the hydroxyl groups at the ribose moiety of the nucleotide. Furthermore, the KdpC subunit was shown to interact with the nucleotide-binding loop of KdpB in an ATP-dependent manner around the ATP-binding pocket, thereby increasing the ATP-binding affinity by the formation of a transient KdpB/KdpC/ATP ternary complex.
authors.affiliation: Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany.
authors.forename: Kristina
authors.initials: K
authors.lastname: Irzik
authors.forename: Juliane
authors.initials: J
authors.lastname: Pfrötzschner
authors.forename: Tatjana
authors.initials: T
authors.lastname: Goss
authors.forename: Franziska
authors.initials: F
authors.lastname: Ahnert
authors.forename: Melina
authors.initials: M
authors.lastname: Haupt
authors.forename: Jörg-Christian
authors.initials: JC
authors.lastname: Greie
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D020816:Amino Acid Motifs; D001665:Binding Sites; D055162:Biocatalysis; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D006860:Hydrogen Bonding; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D010446:Peptide Fragments; D021122:Protein Subunits; D011994:Recombinant Proteins; D005973:Glutamine; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C058166:potassium translocating Kdp-ATPase, E coli