Opsin

Opsin is a protein that, in conjunction with a chromophore, forms a photosensitive system. Opsins are found in the photoreceptor cells of the retina and are crucial for vision. Opsins can also be found in the skin and brain where they are involved in a variety of biological processes.

Structure

Opsins are members of the G protein-coupled receptor (GPCR) superfamily, which contains seven transmembrane domains. The opsin protein covalently binds to a chromophore, typically 11-cis-retinal, through a Schiff base linkage to a lysine residue in the seventh transmembrane domain.

Function

Opsins are crucial for vision. When light hits the chromophore, the energy causes a conformational change in the opsin protein, which triggers a cascade of events leading to an electrical signal being sent to the brain. This process is known as phototransduction.

Opsins are also involved in a variety of other biological processes. For example, they are involved in the regulation of circadian rhythms and the detection of light for the pupillary light reflex.

Types

There are several types of opsins, including rod opsins, cone opsins, and non-visual opsins. Rod opsins are found in the rod cells of the retina and are responsible for vision in low light conditions. Cone opsins are found in the cone cells of the retina and are responsible for color vision. Non-visual opsins are found in the skin and brain and are involved in a variety of biological processes.

Evolution

Opsins are thought to have evolved from a common ancestor, with the different types of opsins diverging over time. This is supported by the fact that all opsins share a common structure and function.

See also

• Photoreceptor cell
• Phototransduction
• G protein-coupled receptor
• Circadian rhythm
• Pupillary light reflex

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