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 (PubMed:15137943). Plays a central role in the host erythrocytes and hepatocytes infection cycles, sexual reproduction and mosquito transmission of the parasite (PubMed:15137943, PubMed:27425827, PubMed:28481199, PubMed:30315162, PubMed:32866196). During the liver stage, involved in sporozoite motility and thus in sporozoite invasion of host hepatocytes, probably together with CDPK1 and CDPK5 (PubMed:27425827, PubMed:32866196). Involved in merosome egress from host hepatocytes, probably together with CDPK5 (PubMed:32866196). During the asexual blood stage, involved in merozoite invasion of host erythrocytes and motility by stabilizing the inner membrane complex, a structure below the plasma membrane which acts as an anchor for the glidosome, an acto-myosin motor (PubMed:30315162). Required for cell cycle progression in the male gametocyte (PubMed:15137943, PubMed:28481199, PubMed:30315162). During male gametogenesis in the mosquito gut, required to initiate the first round of DNA replication, probably by facilitating the assembly of the pre-replicative MCM complex, to assemble the first mitotic spindle and, at the end of gametogenesis, to initiate axoneme motility, cytokinesis and subsequent exflagellation (PubMed:28481199). For each of these steps, may phosphorylate SOC1, SOC2 and SOC3, respectively (PubMed:28481199). Together with CDPK1, regulates ookinete gliding in the mosquito host midgut (PubMed:30315162). During male gametogenesis in the mosquito gut, required to initiate the first round of DNA replication, probably by facilitating the assembly of the pre-replicative MCM complex, and to assemble the first mitotic spindle. At the end of male gametogenesis in the mosquito gut, required to initiate axoneme motility, cytokinesis and subsequent exflagellation. 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 (PubMed:15137943). Upon calcium binding to the EF-hand domains, 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-234, which leads to the kinase activation (By similarity). Intracellular calcium increase is triggered by xanthurenic acid (XA), a small mosquito molecule that induces the differentiation of specialized transmission stages, the gametocytes, into male and female gametes (Probable). Activated by a decrease in temperature (20 degrees Celsius) and an increase in pH (7.6) occurring when the parasite is ingested by in the mosquito (By similarity). May interact with the pre-replication MCM complex prior male gametogenesis activation. A small fraction of the protein localizes to membranes and to chromatin. Expressed in sporozoites and in liver stages (at protein level) (PubMed:27425827). Highly expressed in male gametocytes and exflagellated gametes, and to a lesser extent, in female gametocytes (at protein level) (PubMed:15137943, PubMed:28481199). Expressed in ookinetes (PubMed:15137943). Weakly or not expressed in asexual parasite stages (PubMed:15137943). 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. Myristoylated; myristoylation may target it to different subcellular compartments (PubMed:28481199). During male gametogenesis, myristoylation is required to initiate DNA replication but not for mitotic spindle assembly or axoneme activation (PubMed:28481199). Not palmitoylated. May be autophosphorylated on Thr-234 in vitro. Host hepatocyte invasion is reduced in knockout sporozoites; the few intracellular parasites develop and egress normally (PubMed:27425827). In infected mice, formation of schizonts and merozoite invasion of host erythrocytes are normal (PubMed:30315162). In a PKG T622Q mutant background, reduces ring formation and thus the number of schizonts (PubMed:30315162). In addition, merozoites have a discontinuous inner membrane complex (PubMed:30315162). Impaired exflagellation of male gametocytes which fails to assemble the mitotic spindle and are arrested at the first round of DNA replication (PubMed:28481199). In a PKG T622Q mutant background, male gametocytes fail to exflagellate in the mosquito vector (PubMed:30315162). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily.