rodopsina

Rodopsina is a light-sensitive protein found in the rod cells of the vertebrate retina, playing a crucial role in vision under low-light conditions. This membrane-bound protein belongs to the family of G-protein coupled receptors and contains a cofactor called retinal, which is derived from vitamin A. When photons of light hit rodopsin, it undergoes a conformational change that initiates the visual signal transduction cascade.

The protein consists of seven transmembrane helices connected by three extracellular and three intracellular loops. The retinal molecule is covalently bound to lysine residue 296 in the seventh transmembrane domain through a protonated Schiff base linkage. Upon light absorption, the 11-cis-retinal isomerizes to all-trans-retinal, triggering a series of conformational changes in the protein structure.

Rodopsin is responsible for scotopic vision, which occurs in dim lighting conditions. It is significantly more sensitive to light than cone opsins, allowing humans and other vertebrates to detect light levels as low as a single photon. This extreme sensitivity comes at the cost of color discrimination, as rod cells do not distinguish between different wavelengths of light.

The discovery of rodopsin is attributed to Franz Baly in 1877, though its protein nature was not understood until much later. Mutations in the rodopsin gene can lead to various forms of inherited blindness, including retinitis pigmentosa, a progressive degenerative disease affecting rod and cone photoreceptors. Research on rodopsin has provided fundamental insights into the molecular mechanisms of vision and continues to inform the development of treatments for visual disorders. The protein's structure and function have been extensively studied, making it one of the best-understood G-protein coupled receptors in biology.