CaMKII phosphorylates the C-terminal tail of Cav1.2 Ca²⁺ channel and modulates interaction of the channel with calmodulin

Abstract

Cav1.2 Ca²⁺ channel is suggested to be modulated by calmodulin (CaM) and Ca²⁺/CaM-dependent protein kinase II (CaMKII), that are proposed to underlie Ca²⁺-dependent inactivation and facilitation of channel activity. To explore phosphorylation sites for CaMKII, three GST-fusion fragment peptides derived from the C-terminal tail of guinea-pig Cav1.2, CT-1 (amino acids number 1509-1791), CT-2 (1777-2003) and CT-3 (1944-2169) were examined in vitro. Only CT-1 was consistently phosphorylated by CaMKII. By using mutated CT-1, the phosphorylation site was suggested to be threonine residue at position 1603. In pull-down assay, CT-1 but not CT-2 nor CT-3 was found to interact with CaM at both low and high [Ca²⁺] conditions. CT-1 treated with CaMKII showed a higher affinity for CaM than that treated with alkaline phosphatase. These results suggest that interaction between CT-1 and CaM is modulated by phosphorylation mediated by CaMKII, and that they are consistent with the hypothesis that both CaM and CaMKII are involved in maintaining basal activity of the channel and in Ca²⁺-dependent inactivation and facilitation of the channel. [J Physiol Sci. 2006;56 Suppl:S150]