Calcium/calmodulin-dependent protein kinase belonging to a proposed calcium-triggered signaling cascade involved in a number of cellular processes. Phosphorylates CAMK1 and CAMK4. Phosphorylates CAMK1D (By similarity). Seems to be involved in hippocampal activation of CREB1 (By similarity). Efficiently phosphorylates 5'-AMP-activated protein kinase (AMPK) trimer, including that consisting of PRKAA1, PRKAB1 and PRKAG1. This phosphorylation is stimulated in response to Ca(2+) signals. May play a role in neurite growth. Isoform 2 may promote neurite elongation, while isoform 1 may promoter neurite branching. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by Ca(2+)/calmodulin. Binding of calmodulin may relieve intrasteric autoinhibition. Autophosphorylation does not alter activity or regulation by Ca(2+)/calmodulin. In part, activity is independent on Ca(2+)/calmodulin. Interacts with calmodulin. Predominantly nuclear in unstimulated cells, relocalizes into cytoplasm and neurites after forskolin induction. Mainly expressed in brain, but detected in all tissues tested (at protein level). In the brain, isoform 1 may be predominant. with high levels in the cerebellum and hippocampus, although isoform 3 is detectable. Isoform 3 is also expressed in lung. The autoinhibitory domain overlaps with the calmodulin binding region and may be involved in intrasteric autoinhibition. The RP domain (arginine/proline-rich) is involved in the recognition of CAMKI and CAMK4 as substrates. Phosphorylated by PKA (By similarity). Each isoform may show a different pattern of phosphorylation (By similarity). Autophosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.