Serine/threonine protein kinase which acts as a downstream effector of the second messenger cGMP. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by cGMP (PubMed:11834729, PubMed:11914085). The cGMP-binding domains acts cooperatively to activate PKG (PubMed:11914085). Inhibited by the antiparasitic small molecule 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1Hpyrrol- 3-yl]pyridine (compound 1) (PubMed:11834729). Monomer. Expressed in unsporulated oocysts. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. cGMP subfamily.