CIPK serine-threonine protein kinases interact with CBL proteins. Binding of a CBL protein to the regulatory NAF domain of CIPK protein lead to the activation of the kinase in a calcium-dependent manner. Downstream of CBL1, CBL2, CBL3 and CBL9, regulates by phosphorylation the K(+) conductance and uptake of AKT1. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Part of a K(+)-channel calcium-sensing kinase/phosphatase complex composed by a calcium sensor CBL (CBL1, CBL2, CBL3 or CBL9), a kinase CIPK (CIPK6, CIPK16 or CIPK23), a phosphatase PP2C (AIP1) and a K(+)-channel (AKT1). Interacts with AKT1, CBL1, CBL2, CBL3 and CBL9. The activation loop within the kinase domain is the target of phosphorylation/activation by upstream protein kinases. The PPI motif mediates the interaction with the ABI (abscisic acid-insensitive) phosphatases (By similarity). Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.