a, Evolutionary conservation of the C-terminus in canonical IMPDH1 and both retinal splice variants. b, Surface representation of octamer side view. Dotted box indicates the region shown in c-d. c-d, Each chain is a different color green, C-term residues 510–512 in orange, and IMP in purple. c, inhibited canonical IMPDH1. d, Inhibited retinal variant IMPDH1(546).