CaMKII2 plays a ubiquitous and central role in calcium signaling. Alternative splicing of the four CaMKII genes (␣, ␤, ␥, and ␦) gives rise to ϳ30 known mRNA/protein products. CaMKII␣ and CaMKII␤ predominate in the brain and are involved in normal regulation of synaptic transmission (1-4). Calcium/calmodulin-dependent autophosphorylation at Thr 286 (numbered as in CaMKII␣) enhances the affinity for calcium/calmodulin and confers autonomous (calcium-independent) activity after calmodulin dissociates. Consequently, CaMKII is capable of integrating information conveyed by the amplitude, frequency, and duration of local calcium transients to which it is exposed. Autophosphorylation at Thr 305/306 occurs only in the absence of bound calcium/calmodulin and blocks subsequent calmodulin binding (reviewed in Ref. 5).Knock-in mutation of the Thr 286 or Thr 305/306 autophosphorylation sites in murine CaMKII␣ to Ala or Asp drastically alters some forms of hippocampal synaptic plasticity and disrupts spatial learning behaviors (reviewed in Ref. 6). The specificity of changes in synaptic responses to their dedicated inputs implies that postsynaptic actions of CaMKII, such as modulation of the trafficking and activity of AMPA-type glutamate receptors, are exquisitely regulated in a spatial and temporal manner (7-9).CaMKII interacts with other proteins that we refer to collectively as CaMKII-associated proteins (CaMKAPs). At postsynaptic sites, these include multiple subunits of the N-methyl-D-aspartate-type glutamate receptor (NMDA receptor) (10 -13), densin-180 (14, 15), ␣-actinin (15, 16), cyclin-dependent protein kinase 5 (16), synGAP␤ (17), and filamentous actin (18,19). However, specific contributions of each of these interactions to neuronal signaling and the regulation of synaptic plasticity remain unclear (reviewed in Refs. 7-9). To specifically address this issue, it is critical to have a thorough understanding of the molecular bases for these interactions and the factors regulating complex formation.Prior studies have identified dissimilar high affinity CaMKII-binding domains in the NR2B subunit of the NMDA receptor and in densin-180. These interactions are differentially regulated by calcium/calmodulinbinding, autophosphorylation at Thr 286 , and phosphorylation of the binding proteins (10, 11, 13-15, 20, 21). Moreover, densin-180 and NR2B do not compete with each other for binding to CaMKII (14). Interestingly, densin-180 makes an additional direct interaction with ␣-actinin (15), and ␣-actinin can bind to the NR1 and NR2B subunits of the NMDA receptor (21-24). However, little is known about the molecular determinants for CaMKII binding to ␣-actinin. Here, we report an initial molecular dissection of the CaMKII-binding domain in ␣-actinin-2 and explore the relationship of this interaction to CaMKII binding with densin-180 and NR2B. The data indicate that CaMKII itself may serve as a structural scaffold for the assembly of a postsynaptic signalosome. MATERIALS AND METHODSAntibodies-Western blotting was performed wit...

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We previously characterized PP1bp134 and PP1bp175, two neuronal proteins that bind the protein phosphatase 1 catalytic subunit (PP1). Here we purify from rat brain actin-cytoskeletal extracts PP1 A holoenzymes selectively enriched in PP1␥ 1 over PP1␤ isoforms and also containing PP1bp134 and PP1bp175. PP1bp134 and PP1bp175 were identified as the synapse-localized Factin-binding proteins spinophilin (Allen, P. B., Ouimet, C. C., and Greengard, P. (

Background-Activation of cellular Ca2ϩ signaling molecules appears to be a fundamental step in the progression of cardiomyopathy and arrhythmias. Myocardial overexpression of the constitutively active Ca 2ϩ -dependent phosphatase calcineurin (CAN) causes severe cardiomyopathy marked by left ventricular (LV) dysfunction, arrhythmias, and increased mortality rate, but CAN antagonist drugs primarily reduce hypertrophy without improving LV function or risk of death. Methods and Results-We found that activity and expression of a second Ca