Although the structures of CNGA1 and CNGA3 were generally similar, they were not identical. As stated above, different residue positions were used in the helical packing between the two heptad repeat regions in the sequence. In addition, the supercoiling was different between CNGA1 and CNGA3, with a somewhat longer pitch for CNGA1 (181 Å) than for CNGA3 (149 Å) (Supplementary Table S2 ). These differences were also reflected in the structural alignments of the individual subunits of CNGA1 and CNGA3 (rmsd of Cα ranging from 0.87 Å to 2.0 Å). These differences in structure, however, do not have any known functional consequences.