Figure 3.
Lys-94 is essential for UV (UV-A) reception and transmission by Platynereis c-opsin. A, amino acid sequence alignment of opsins around position 94 in the second transmembrane helix. Position 94 is highlighted in boldface, and positions 86, 89, and 90 are also indicated. Lys-94 in Platynereis c-opsin is highlighted in red. UV-sensitive opsins are labeled UV. Lys-90 in Drosophila Rh3 can be regarded as Lys-89 because of a gap at the site. B, arrangement of 11-cis-retinal and position 94 in the second transmembrane helix. 11-cis-retinal (yellow) and positions 94 as well as 86, 89, and 90 (red spheres) in the crystal structure of bovine rhodopsin (Protein Data Bank code 1U19) (48) are shown. Lys-296, which forms the retinal Schiff base linkage, is also shown. C–J, absorption spectra of the Platynereis c-opsin mutants K94T (C), K94A (D), K94S (E), K94V (F), K94D (G), K94E (H), K94H (I), and K94R (J). The λmax values of the mutants are indicated. K–M, spectral changes of Platynereis c-opsin mutants K94T, K94A, and K94S upon light illumination. The absorption spectra of the Platynereis c-opsin mutants K94T (K), K94A (L), and K94S (M) in the dark (black), after illumination with blue (440 nm) light (red), and after subsequent illumination with orange-red (>580 nm) light (blue). N and O, photo-induced changes of current amplitudes at −100 mV from Xenopus oocytes expressing Platynereis c-opsin WT (N) or the K94T mutant (O). Illumination with UV (violet bar) and yellow light (>480 nm, orange bar) is indicated, and the black bar indicates that the oocytes were kept in the dark. P, comparison of photo-induced currents by Platynereis c-opsin WT and the K94T mutant. Differences in current amplitudes at −100 mV before and after light illumination are plotted. The error bars represent S.D. values (n = 9 for WT and n = 5 for K94T). Q, photo-induced changes of current amplitude at −100 mV from a Xenopus oocyte expressing the Platynereis c-opsin K94T mutant. The oocyte is illuminated by yellow (>480 nm) light followed by UV light.