Potent and specific cellular inhibitor of CaM-kinase II (CAMK2) (By similarity). Traps Ca(2+)/calmodulin on CAMK2 (By similarity). Interacts with CAMK2A and CAMK2B in the presence of Ca(2+)/calmodulin or after autophosphorylation. Excluded from nucleus when coexpressed with activated CAMK2. Belongs to the CAMK2N family.