Figure 3. Harmonin binding is reduced by disruption of the PDZ-binding site in the α₁1.3 dCT.

A, schematic diagram of harmonin and α₁1.3. The long C-terminal domain encoded by exon 42 (Ex42) includes the PDZ-binding motif (ITTL) that interacts with the second of three PDZ domains of harmonin. The coiled-coil domain (CC) that is deleted in the dfcr harmonin mutant is indicated. The ‘x’ marks approximate location of truncation of the dCT due to inclusion of exon 42A. B, coimmunoprecipitation of harmonin with Ca_v1.3 channels in transfected HEK293T cells. Cells were transfected with harmonin alone (control) or cotransfected with Ca_v1.3 subunits including α₁1.3 with full-length (Ex42) or truncated (Ex42A) dCT or α₁1.3 with terminal leucine substituted with alanine (L-A). Western blotting detected α₁1.3 (upper panel) and coimmunoprecipitated harmonin (lower panel). C, quantification reflecting percentage change in harmonin coimmunoprecipitated with α₁1.3_Ex42A and α₁1.3_L-A compared to that for α₁1.3_Ex42 (%co-ip harmonin). See Methods for details.