A key amino acid site associated with rhodopsin mammal evolution to diurnal vision.

Rhodopsin is a photoreceptor protein found in the vertebrate retina used as a landmark for vision evolution studies at the molecular level. Here, we examined the biochemical and functional performance of modern rhodopsin from three different mammal species- bovine, murine and human-to analyze their visual pigment evolutionary relationships. We selected these species for their relevance in vision research, their different position on the phylogenetic tree and their diverse ethology regarding nocturnal (mouse) and diurnal (bovine and human) life. We report on the important role of the amino acid at position 290 as a key player in the active rhodopsin conformation stability. Our spectroscopic analysis shows that the retinal release process for mouse rhodopsin (L290) is significantly slower, meaning a more stable and durable active state, compared to the human and bovine cases (I290). This finding is supported by the faster retinal release rate observed in the L290I mutant mouse rhodopsin, where the nocturnal mutated pigment behaved like diurnal rhodopsin. The result suggests a potential link between the amino acid at this position and the activity pattern (nocturnal or diurnal). This association was also observed when comparing the sequences of 79 mammal species at position 290, and better appreciated in more specialized primate and rodent orders. Moreover, we propose an evolutionary mechanism in rhodopsin specialization for diurnal and nocturnal life, implying a compromise between the prevalence of damage protection under bright light in nocturnal therian mammals (L290) and dark adaptation under dim light in diurnal therian mammals (I290).