Part of the high-affinity ATP-driven potassium transport (or Kdp) system, which catalyzes the hydrolysis of ATP coupled with the electrogenic transport of potassium into the cytoplasm. This subunit is responsible for energy coupling to the transport system and for the release of the potassium ions to the cytoplasm (By similarity). The Kdp system is essential for growth under K(+) limitation, and for survival under desiccation and salt crystal inclusion (PubMed:18633573, PubMed:23757278). ATP + H2O + K(+)(out) = ADP + H(+) + K(+)(in) + phosphate The system is composed of three essential subunits: KdpA, KdpB and KdpC. The complex also contains KdpF, a small non-essential subunit. Up-regulated in response to K(+) limitation (PubMed:18633573, PubMed:21947979). Induced under desiccating conditions (PubMed:23757278). kdpFABCQ and kdpFABC deletion strains are only able to grow in the presence of K(+) concentrations above 60 uM. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IA subfamily.