Protection of α-CaMKII from Dephosphorylation by GluN2B Subunit of NMDA Receptor Is Abolished by Mutation of Glu96 or His282 of α-CaMKII

Role of Ca2+/Calmodulin-Dependent Protein Kinase Type II in Mediating Function and Dysfunction at Glutamatergic Synapses

Glutamatergic synapses harbor abundant amounts of the multifunctional Ca²⁺/calmodulin-dependent protein kinase type II (CaMKII). Both in the postsynaptic density as well as in the cytosolic compartment of postsynaptic terminals, CaMKII plays major roles. In addition to its Ca²⁺-stimulated kinase activity, it can also bind to a variety of membrane proteins at the synapse and thus exert spatially restricted activity. The abundance of CaMKII in glutamatergic synapse is akin to scaffolding proteins although its prominent function still appears to be that of a kinase. The multimeric structure of CaMKII also confers several functional capabilities on the enzyme. The versatility of the enzyme has prompted hypotheses proposing several roles for the enzyme such as Ca²⁺ signal transduction, memory molecule function and scaffolding. The article will review the multiple roles played by CaMKII in glutamatergic synapses and how they are affected in disease conditions.

Glu60 of α-Calcium/calmodulin dependent protein kinase II mediates crosstalk between the regulatory T-site and protein substrate binding region of the active site

Memory formation transpires to be by activation and persistent modification of synapses. A chain of biochemical events accompany synaptic activation and culminate in memory formation. These biochemical events are steered by interplay and modulation of various synaptic proteins, achieved by conformational changes and phosphorylation/dephosphorylation of these proteins. Calcium/calmodulin dependent protein kinase II (CaMKII) and N-methyl-d-aspartate receptors (NMDARs) are synaptic proteins whose interactions play a pivotal role in learning and memory process. Catalytic activity of CaMKII is modulated upon its interaction with the GluN2B subunit of NMDAR. The structural basis of this interaction is not clearly understood. We have investigated the role of Glu⁶⁰ of α-CaMKII, a conserved residue present in the ATP binding region of kinases, in the regulation of catalysis of CaMKII by GluN2B. Mutation of Glu⁶⁰ to Gly exerts different effects on the kinetic parameters of phosphorylation of GluN2B and GluN2A, of which only GluN2B binds to the T-site of CaMKII. GluN2B induced modulation of the kinetic parameters of peptide substrate was altered in the E60G mutant. The mutation almost abolished the modulation of the apparent K_m value for protein substrate. However, although kinetic parameters for ATP were altered by mutating Glu⁶⁰, modulation of the apparent K_m value for ATP by GluN2B seen in WT was exhibited by the E60G mutant of α-CaMKII. Hence our results posit that the communication of the T-site of CaMKII with protein substrate binding region of active site is mediated through Glu⁶⁰ while the communication of the T-site with the ATP binding region is not entirely dependent on Glu⁶⁰.

All-trans retinoic acid attenuates isoproterenol-induced cardiac dysfunction through Crabp1 to dampen CaMKII activation

Inhibiting Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) over activation can decrease detrimental cardiac remodeling that leads to dilated cardiomyopathy, cell death, and heart failure. We previously showed that cellular retinoic acid binding protein 1 (Crabp1) knockout mice (CKO) exhibited a more severe isoproterenol (ISO)-induced heart failure and cardiac remodeling phenotype with elevated CaMKII activity in the heart, suggesting a cardiac-protective function of Crabp1 through modulating CaMKII activity. Here we examine whether the highly selective, endogenous ligand of Crabp1, all-trans retinoic acid (RA), can attenuate ISO-induced cardiac dysfunction. We also examine if this attenuation involves Crabp1 and the inhibition of CaMKII. RA pre-treatment followed by ISO challenge effectively restores ejection fraction in wild type, but not in CKO mice. This is correlated with reduced CaMKII auto-phosphorylation at T287 and phospholamban phosphorylation at T17, a substrate of CaMKII. RA pretreatment also reduces ISO-induced apoptosis in WT heart. Cell culture experiments confirm that RA inhibits CaMKII phosphorylation, which requires Crabp1. Molecular data reveal interaction of Crabp1 with the kinase and regulatory domains of CaMKII, and that RA selectively enhances Crabp1 interaction with the regulatory domain, suggesting a potential regulatory role for holo-Crabp1 in CaMKII activation. Together, these data demonstrate that RA bound Crabp1 plays a protective role in β-adrenergic stimulated cardiac remodeling, which is partially attributed to its dampening CaMKII activation. Targeting Crabp1 provides a potentially new therapeutic strategy for managing heart diseases.