Neuronal CaMKII acts as a structural kinase.

CaMKII, calcium/calmodulin dependent protein kinase, is an active kinase in the cell that phosphorylates a number of substrates including several cytoskeletal and signaling proteins. In addition to kinase activity, the beta isoform of CaMKII also contains an F-actin binding region. We recently identified a new F-actin rich structure in developing cortical neurons that endogenous CaMKIIbeta bound. In nonneuronal cells and dendrite spines of hippocampal neurons where an interaction between CaMKIIbeta and F-actin has been identified, CaMKIIbeta was involved in regulating the differentiation of dendrite spines and formation of synapses. In this study, we took advantage of the temporal and spatial regulation of CaMKII isoforms to reveal a specific role for CaMKIIbeta in binding and stability of a novel F-actin rich structure. We used FRAP and colocalization assays in this CaMKIIbeta rich system to demonstrate a structural, rather than enzymatic, role of CaMKIIbeta. In this addendum, we further discuss the significance of this study and the possible implication to the field.