Figure 2.

Common structure of the alpha 1 subunit of voltage-operated calcium channels. The main, pore-forming α₁ subunits of the various voltage-operated calcium channels share a common general structure, with four homologous repeats (I–IV), each composed of six hydrophobic, putative membrane-spanning alpha helix domains (S1–S6). The three large loops connecting repeats together, as well as the N- and C-terminal extremities are located in the cytosol. The positions of Gly403 and Ile770 mutated in CACNA1D (13), and of Met1549 in CACNA1H (35), are indicated at the end of the S6 segments in repeats I, II, and III, respectively.