Calmodulin promotes a Ca 2+ -dependent conformational change in the C-terminal regulatory domain of Ca V 1.2.

Calmodulin (CaM) binds to the membrane-proximal cytosolic C-terminal domain of Ca V 1.2 (residues 1520-1669, CT(1520-1669)) and causes Ca 2+ -induced conformational changes that promote Ca 2+ -dependent channel inactivation (CDI). We report biophysical studies that probe the structural interaction between CT(1520-1669) and CaM. The recombinantly expressed CT(1520-1669) is insoluble, but can be solubilized in the presence of Ca 2+ -saturated CaM (Ca 4 /CaM), but not in the presence of Ca 2+ -free CaM (apoCaM). We show that half-calcified CaM (Ca 2 /CaM 12 ) forms a complex with CT(1520-1669) that is less soluble than CT(1520-1669) bound to Ca 4 /CaM. The NMR spectrum of CT(1520-1669) reveals spectral differences caused by the binding of Ca 2 /CaM 12 versus Ca 4 /CaM, suggesting that the binding of Ca 2+ to the CaM N-lobe may induce a conformational change in CT(1520-1669).