# A repertoire of visible light–sensitive opsins in the deep-sea hydrothermal vent shrimp Rimicaris hybisae

## TL;DR

This study explores how a deep-sea shrimp detects dim light using specialized proteins called opsins, which are adapted to the unique light conditions of hydrothermal vents.

## Contribution

The paper identifies a unique visible light-sensitive opsin repertoire in Rimicaris hybisae, including a novel Opn5 with a distinct light sensitivity mechanism.

## Key findings

- Rimicaris hybisae has six opsins, including a visible light-sensitive Opn5 with a unique protonated Schiff base stabilization mechanism.
- Five opsins show light-dependent G protein activity, while peropsin functions like photoisomerases.
- The shrimp's opsins are adapted to detect visible light (457–517 nm), unlike most Opn5 opsins that are UV-sensitive.

## Abstract

Unlike terrestrial environments, where humans reside, there is no sunlight in the deep sea. Instead, dim visible light from black-body radiation and bioluminescence illuminates hydrothermal vent areas in the deep sea. A deep-sea hydrothermal vent shrimp, Rimicaris hybisae, is thought to detect this dim light using its enlarged dorsal eye; however, the molecular basis of its photoreception remains unexplored. Here, we characterized the molecular properties of opsins, universal photoreceptive proteins in animals, found in R. hybisae. Transcriptomic analysis identified six opsins: three Gq-coupled opsins, one Opn3, one Opn5, and one peropsin. Functional analysis revealed that five of these opsins exhibited light-dependent G protein activity, whereas peropsin exhibited the ability to convert all-trans-retinal to 11-cis-retinal like photoisomerases. Notably, all the R. hybisae opsins, including Opn5, convergently show visible light sensitivity (around 457–517 nm), whereas most opsins categorized as Opn5 have been demonstrated to be UV sensitive. Mutational analysis revealed that the unique visible light sensitivity of R. hybisae Opn5 is achieved through the stabilization of a protonated Schiff base by a counterion residue at position 83 (Asp83), which differs from the position identified in other opsins. These findings suggest that the vent shrimp R. hybisae has adapted its photoreceptive devices to dim deep-sea hydrothermal light by selectively maintaining a repertoire of visible light–sensitive opsins, including the uniquely tuned Opn5.