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 acts as a catalytic chaperone that increases the ATP-binding affinity of the ATP-hydrolyzing subunit KdpB by the formation of a transient KdpB/KdpC/ATP ternary complex (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). 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 KdpC family.