Ca
2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylates the
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2a subunit ofvoltage-gated Ca
2+ channels at Thr498 to facilitate cardiac L-type Ca
2+ channels. CaMKII colocalizeswith
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2a in cardiomyocytes and also binds to a domain in
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2a that contains Thr498 and exhibits an aminoacid sequence similarity to the CaMKII autoinhibitory domain and to a CaMKII binding domain in theNMDA receptor NR2B subunit (Grueter, C. E. et al. (2
006)
Mol. Cell 23, 641). Here, we explore theselectivity of the actions of CaMKII among Ca
2+ channel
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1b,
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2a,
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3, and
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4 isoforms with similar initial rates and final stoichiometries of 6-12 mol of phosphateper mol of protein. However, activated/autophosphorylated CaMKII binds to
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1b and
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2a with a similarapparent affinity but does not bind to
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3 or
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4. Prephosphorylation of
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1b and
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2a by CaMKII substantiallyreduces the binding of autophosphorylated CaMKII. Residues surrounding Thr498 in
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2a are highlyconserved in
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1b but are different in
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3 and
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4. Site-directed mutagenesis of this domain in
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2a showedthat Thr498 phosphorylation promotes dissociation of CaMKII-
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2a complexes in vitro and reducesinteractions of CaMKII with
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2a in cells. Mutagenesis of Leu493 to Ala substantially reduces CaMKIIbinding in vitro and in intact cells but does not interfere with
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2a phosphorylation at Thr498. In combination,these data show that phosphorylation dynamically regulates the interactions of specific isoforms of theCa
2+ channel
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