The Ca2+-dependent interaction of calpastatin domain L with the C-terminal tail of the Cav1.2 channel

To demonstrate the interaction of calpastatin (CS) domain L (CSL) with Cav1.2 channel, we investigated the binding of CSL with various C-terminus-derived peptides at ≈ free, 100 nM, 10 μM, and 1 mM Ca2+ by using the GST pull-down assay method. Besides binding with the IQ motif, CSL was also found to bind with the PreIQ motif. With increasing [Ca2+], the affinity of the CSL-IQ interaction gradually decreased, and the affinity of the CSL-PreIQ binding gradually increased. The results suggest that CSL may bind with both the IQ and PreIQ motifs of the Cav1.2 channel in different Ca2+-dependent manners.