UC Davis

Calmodulin (CaM) binds to the membrane-proximal cytosolic C-terminal domain of Ca_V 1.2 (residues 1520-1669, CT(1520-1669)) and causes Ca²⁺ -induced conformational changes that promote Ca²⁺ -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 Ca²⁺ -saturated CaM (Ca₄ /CaM), but not in the presence of Ca²⁺ -free CaM (apoCaM). We show that half-calcified CaM (Ca₂ /CaM₁₂ ) forms a complex with CT(1520-1669) that is less soluble than CT(1520-1669) bound to Ca₄ /CaM. The NMR spectrum of CT(1520-1669) reveals spectral differences caused by the binding of Ca₂ /CaM₁₂ versus Ca₄ /CaM, suggesting that the binding of Ca²⁺ to the CaM N-lobe may induce a conformational change in CT(1520-1669).