Anion sensitivity and spectral tuning of middle- and long-wavelength-sensitive (MWS/LWS) visual pigments

Abstract

The long-wavelength-sensitive (LWS) opsins form one of four classes of vertebrate cone visual pigment and exhibit peak spectral sensitivities (λ(max)) that generally range from 525 to 560 nm for rhodopsin/vitamin-A(1) photopigments. Unique amongst the opsin classes, many LWS pigments show anion sensitivity through the interaction of chloride ions with a histidine residue at site 197 (H197) to give a long-wavelength spectral shift in peak sensitivity. Although it has been shown that amino acid substitutions at five sites (180, 197, 277, 285 and 308) are useful in predicting the λ(max) values of the LWS pigment class, some species, such as the elephant shark and most marine mammals, express LWS opsins that possess λ(max) values that are not consistent with this 'five-site' rule, indicating that other interactions may be involved. This study has taken advantage of the natural mutation at the chloride-binding site in the mouse LWS pigment. Through the use of a number of mutant pigments generated by site-directed mutagenesis, a new model has been formulated that takes into account the role of charge and steric properties of the side chains of residues at sites 197 and 308 in the function of the chloride-binding site in determining the peak sensitivity of LWS photopigments.

Three cone opsin genes determine the properties of the visual spectra in the Japanese anchovy Engraulis japonicus (Engraulidae, Teleostei)

“…In EJ-LWS, these sites were occupied by AHYTA residues and the predicted λ max was 553nm, longer than our measurement. Davies et al (Davies et al, 2009;Davies et al, 2012) reported that the λ max value of elephant shark Callorhinchus milii LWS1 (EF565165) expressed in an in vitro experiment was not consistent with the 'five-site' rule, because of inactivation of the chloride ion positive charge of H197 caused by amino acid substitution of A308S. The EJ-LWS has amino acid residues H and A at sites 197 and 308 and our present knowledge could not explain the molecular mechanisms involved in the blue shift.…”

Cone monochromacy and visual pigment spectral tuning in wobbegong sharks

“…The tuning sites of the RH1 pigment in both species of wobbegongs are identical to each other and to the bovine sequence at all but sites 292 and 299 (table 1). The O. maculatus sequence encodes an Ala292Ser substitution, which is known to cause a 10 nm short-wavelength shift in the l max [16,18,19]. This is consistent with the spectral absorbance of the O. maculatus rod pigment, which has a l max at 484 nm compared with 498 nm for O. ornatus (figure 1) [7].…”

Molecular ecology and adaptation of visual photopigments in craniates

“…An exception is found in the mouse, Mus musculus , where the λ max is short‐wavelength‐shifted by around 28 to ∼510 nm due to the loss of the chloride‐binding site (Sun et al. 1997; Davies et al. 2012b) (Table 1).…”