Multivalent interactions of calcium/calmodulin-dependent protein kinase II with the postsynaptic density proteins NR2B, densin-180, and α-actinin-2

Dendritic calcium/ calmodulin- dependent protein kinase II ( CaMKII) is dynamically targeted to the synapse. We show that CaMKII alpha is associated with the CaMKII- binding proteins densin-180, the N- methyl- D- aspartate receptor NR2B subunit, and alpha- actinin in postsynaptic density- enriched rat brain fractions. Residues 819 - 894 within the C- terminal domain of alpha- actinin- 2 constitute the minimal CaMKII- binding domain. Similar amounts of Thr(286)-autophosphorylated CaMKII alpha holoenzyme [ P- T-286] CaMKII bind to alpha- actinin- 2 as bind to NR2B ( residues 1260 - 1339) or to densin-180 ( residues 1247 - 1495) in glutathione- agarose cosedimentation assays, even though the CaMKII- binding domains share no amino acid sequence similarity. Like NR2B, alpha- actinin- 2 binds to representative splice variants of each CaMKII gene ( alpha, beta, gamma, and delta), whereas densin- 180 binds selectively to CaMKII alpha. In addition, C- terminal truncated CaMKII alpha monomers can interact with NR2B and alpha- actinin- 2, but not with densin- 180. Soluble alpha- actinin- 2 does not compete for [ P- T-286] CaMKII binding to immobilized densin-180 or NR2B. However, soluble densin- 180, but not soluble NR2B, increases CaMKII binding to immobilized alpha- actinin- 2 by approximate to 10- fold in a PDZ domain- dependent manner. A His(6)- tagged NR2B fragment associates with GST- densin or GST- actinin but only in the presence of [ P- T-286] CaMKII. Similarly, His6- tagged densin- 180 or alpha- actinin fragments associate with GST- NR2B in a[ P-T-286] CaMKII-dependent manner. In addition, GST- NR2B and His(6)- tagged alpha- actinin can bind simultaneously to monomeric CaMKII subunits. In combination, these data support a model in which [ P-T-286] CaMKII alpha can simultaneously interact with multiple dendritic spine proteins, possibly stabilizing the synaptic localization of CaMKII and/ or nucleating a multiprotein synaptic signaling complex.