Recoverin is a 23 kilodalton (kDa) neuronal calcium-binding protein that is primarily detected in the photoreceptor cells of the eye. It plays a key role in the inhibition of rhodopsin kinase

Rhodopsin kinase

Rhodopsin kinase is a serine/threonine-specific protein kinase involved in phototransduction.-See also:* Rhodopsin* Beta adrenergic receptor kinase* G-protein coupled receptor kinases-External links:...

, a molecule which regulates the phosphorylation

Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

 of rhodopsin

Rhodopsin

Rhodopsin, also known as visual purple, is a biological pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light,...

. A reduction in this inhibition helps regulate sensory adaptation in the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

, since the light-dependent channel closure in photoreceptors causes calcium levels to decrease, which relieves the inhibition of rhodopsin kinase by calcium-bound recoverin, leading to a more rapid inactivation of metarhodopsin II (activated form of rhodopsin).

Structure & Function

Recoverin is involved in the recovery phase of visual excitation and in adaptation to background light. It controls the life span of photoexcited rhodopsin by helping to inhibit rhodopsin kinase. An image of bovine recoverin with 3.00 Å resolution is shown. . This three-dimensional structure was determined by X-ray diffraction. Covalently attached at the amino-terminal of recoverin is a myristoyl group. When the protein binds calcium ions, it undergoes a conformational change and brings out the myristoyl group from the binding portion so that the group is able to either interact with the target or the protein can move to a different region. When recoverin is not bound to calcium, it stays in cytosol. When recoverin binds calcium, it migrates to the disc membrane and is embedded into the membrane using the myristoyl group to anchor itself. This calcium-bound form of recoverin slows the activity of rhodopsin kinase, resulting in the prolongation of light sensitivity for rhodopsin. Recent publications point out additional functions for recoverin. For instance, it goes through a light-dependent intracellular translocation to rod synaptic terminals and improves the signal transfer between rods and rod bipolar cells in the retina of mice.
In humans, the recoverin protein is encoded by the RCVRN gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.