May play a role in signal transduction pathways that involve calcium as a second messenger. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by calcium and calmodulin. Autophosphorylation may play an important role in the regulation of the kinase activity (By similarity). Binds calmodulin (CaM) in a calcium-dependent manner. There are 3 contiguous domains conserved in the CDPK subfamily: a kinase domain, an autoinhibitory (junction) domain and a calmodulin-like domain. The autoinhibitory domain (408-438) inactivates kinase activity under calcium-free conditions (By similarity). Autophosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily.