Figure 1

Schematic diagram of an LWS opsin, with each circle representing an amino acid residue. The portion of the guppy opsins isolated in this study is shaded grey. Sites found to be variable among the guppy opsins that were targeted in Franke et al.'s mutagenesis study of transducin activation capacity [48] are green with diagonal hatching. Those shown to be involved in spectral tuning [6, 45-47] are marked in red with vertical hatching. All other variable sites in the guppy opsins are shaded black. All amino acid numbering follows the human LWS opsins. The cytoplasmic (CM) and extracellular (EM) membranes, the transmembrane domain (TD), and the three extracellular (E1–E3) and four cytoplasmic (C1–C4) loops are indicated. Transmembrane boundaries were inferred by analogy to those of the bovine rhodopsin crystal structure [65].