ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Binds 3 Ca(2+) ions per C2 domain. Belongs to the protein kinase superfamily. TKL Ser/Thr protein kinase family.