Abstract
The molecular mechanisms that regulate invertebrate visual pigment absorption are poorly understood. Through sequence analysis and functional investigation of vertebrate visual pigments, numerous amino acid substitutions important for this adaptive process have been identified. Here we describe a serine/alanine (S/A) substitution in long wavelength-absorbing Drosophila visual pigments that occurs at a site corresponding to Ala-292 in bovine rhodopsin. This S/A substitution accounts for a 10-17-nm absorption shift in visual pigments of this class. Additionally, we demonstrate that substitution of a cysteine at the same site, as occurs in the blue-absorbing Rh5 pigment, accounts for a 4-nm shift. Substitutions at this site are the first spectrally significant amino acid changes to be identified for invertebrate pigments sensitive to visible light and are the first evidence of a conserved tuning mechanism in vertebrate and invertebrate pigments of this class.
Highlights
Organisms use color vision for survival behaviors such as foraging, mating, and predator avoidance [1,2,3]
The As the result of this analysis, we identified an amino acid structure was minimized 5000 steps using NAMD [22] and substitution within the Drosophila opsins that corresponds to a aligned to bovine rhodopsin (PDB entry 1U19) [23] using spectral tuning site identified in the vertebrate pigments at STRAP [24]
We examined the region of the squid rhodopsin chromophore binding site and found that, similar to the three Drosophila models, the residue corresponding to Ala-315 in Rh1 is in close proximity to the Schiff base nitrogen (Fig. 3g)
Summary
Electrophysiology and Microspectrophotometry—Spectral sensitivity was measured as described previously [9]. To investigate the role that this amino acid substitution plays in tuning the spectral properties of invertebrate pigments, we constructed mutant forms of the blue-absorbing (Rh1) and green-absorbing (Rh6) Drosophila opsins, as described previously [9]. In these mutant forms, we replaced the residue in one pigment with the corresponding residue found in the other (i.e. Rh1 A315S and Rh6 S313A). We were unable to record a difference spectrum from transgenic animals expressing the Rh6 S313A construct, consistent with previous studies of unmodified Rh6 [17] These results indicate that this amino acid substitution is important for regulating the tuning of both R-form and M-form absorption.
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