Calcium-dependent protein kinase which acts as a sensor and effector of intracellular Ca(2+) levels probably in part downstream of cGMP-activated PKG kinase (By similarity). In the mosquito midgut, regulates the gliding motility of the ookinete which is essential for the ookinete to invade the midgut epithelium. However, another study showed that while required for ookinete invasion of the midgut epithelium, is not required for ookinete gliding motility (By similarity). 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. Upon calcium binding to the EF-hand domain 2, the C-terminus of the junction domain (J domain) undergoes a conformational change which results in the dissociation of the pseudo-substrate inhibitory motif from the catalytic domain (By similarity). This, in turn, may facilitate the autophosphorylation of the activation loop at Thr-273, which leads to the kinase activation (By similarity). The EF-hand domain 1 cannot bind calcium due to the presence of a Lys instead of an Asp at position 429 and a Gln instead of a Glu at position 436 preventing calcium binding. The EF-hand domains 3 probably binds calcium constitutively when calcium levels are low, while the EF-hand domain 2 binds calcium following an increase in calcium levels. The junction domain (J domain) is composed of 2 motifs that maintain the kinase inactive. The N-terminal autoinhibitory motif acts as a pseudosubstrate inhibiting the catalytic domain while the C-terminal motif binds the EF-hand domains. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily. Orthologs in other Plasmodium species contain 4 EF-hand domains instead of 3 EF-hand domains as identified for this entry, therefore it might be possible that the displayed C-terminus sequence of P.yoelii CDPK3 is incorrect.