Rhodopsin is a light-sensitive receptor protein involved in visual phototransduction. It is named after ancient Greek ῥόδον for rose, due to its pinkish color, and ὄψις for sight. Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). It belongs to a group of photoswitchable opsins. Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 30 minutes, after which rods are more sensitive.
Achromatopsia, also known as total color blindness, is a medical syndrome that exhibits symptoms relating to at least five conditions. The term may refer to acquired conditions such as cerebral achromatopsia, but it typically refers to an autosomal recessive congenital color vision condition, the inability to perceive color and to achieve satisfactory visual acuity at high light levels, typically exterior daylight. The syndrome is also present in an incomplete form which is more properly defined as dyschromatopsia. It is estimated to affect 1 in 30,000 live births worldwide.
Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. Symptoms include trouble seeing at night and decreased peripheral vision. As peripheral vision worsens, people may experience "tunnel vision". Complete blindness is uncommon. Onset of symptoms is generally gradual and often in childhood.
Transducin (Gt) is a protein naturally expressed in vertebrate retina rods and cones and it is very important in vertebrate phototransduction. It is a type of heterotrimeric G-protein with different α subunits in rod and cone photoreceptors.
Cyclic nucleotide–gated ion channels or CNG channels are ion channels that function in response to the binding of cyclic nucleotides. CNG channels are nonselective cation channels that are found in the membranes of various tissue and cell types, and are significant in sensory transduction as well as cellular development. Their function can be the result of a combination of the binding of cyclic nucleotides and either a depolarization or a hyperpolarization event. Initially discovered in the cells that make up the retina of the eye, CNG channels have been found in many different cell types across both the animal and the plant kingdoms. CNG channels have a very complex structure with various subunits and domains that play a critical role in their function. CNG channels are significant in the function of various sensory pathways including vision and olfaction, as well as in other key cellular functions such as hormone release and chemotaxis. CNG channels have also been found to exist in prokaryotes, including many spirochaeta, though their precise role in bacterial physiology remains unknown.
Visual phototransduction is the sensory transduction of the visual system. It is a process by which light is converted into electrical signals in the rod cells, cone cells and photosensitive ganglion cells of the retina of the eye. This cycle was elucidated by George Wald (1906–1997) for which he received the Nobel Prize in 1967. It is so called "Wald's Visual Cycle" after him.
Rod cGMP-specific 3',5'-cyclic phosphodiesterase subunit beta is the beta subunit of the protein complex PDE6 that is encoded by the PDE6B gene. PDE6 is crucial in transmission and amplification of visual signal. The existence of this beta subunit is essential for normal PDE6 functioning. Mutations in this subunit are responsible for retinal degeneration such as retinitis pigmentosa or congenital stationary night blindness.
Cyclic nucleotide-gated cation channel alpha-3 is a protein that in humans is encoded by the CNGA3 gene.
Guanine nucleotide-binding protein G(t) subunit alpha-2 is a protein that in humans is encoded by the GNAT2 gene.
Retinal rod rhodopsin-sensitive cGMP 3',5'-cyclic phosphodiesterase subunit gamma is an enzyme that in humans is encoded by the PDE6G gene.
Guanine nucleotide-binding protein G(t) subunit alpha-1 is a protein that in humans is encoded by the GNAT1 gene.
Cyclic nucleotide gated channel beta 3, also known as CNGB3, is a human gene encoding an ion channel protein.
Rod outer segment membrane protein 1 is a protein that in humans is encoded by the ROM1 gene.
Retinal rod rhodopsin-sensitive cGMP 3',5'-cyclic phosphodiesterase subunit delta is an enzyme that in humans is encoded by the PDE6D gene. PDE6D was originally identified as a fourth subunit of rod cell-specific cGMP phosphodiesterase (PDE). The precise function of PDE delta subunit in the rod specific GMP-PDE complex is unclear. In addition, PDE delta subunit is not confined to photoreceptor cells but is widely distributed in different tissues. PDE delta subunit is thought to be a specific soluble transport factor for certain prenylated proteins and Arl2-GTP a regulator of PDE-mediated transport.
Cyclic nucleotide gated channel beta 1, also known as CNGB1, is a human gene encoding an ion channel protein.
Rod cGMP-specific 3',5'-cyclic phosphodiesterase subunit alpha is an enzyme that in humans is encoded by the PDE6A gene.
Cyclic nucleotide gated channel alpha 2, also known as CNGA2, is a human gene encoding an ion channel protein.
Cyclic nucleotide-gated cation channel alpha-4 is a protein that in humans is encoded by the CNGA4 gene.
Proteins that bind cyclic nucleotides share a structural domain of about 120 residues. The best studied of these proteins is the prokaryotic catabolite gene activator where such a domain is known to be composed of three alpha-helices and a distinctive eight-stranded, antiparallel beta-barrel structure. There are six invariant amino acids in this domain, three of which are glycine residues that are thought to be essential for maintenance of the structural integrity of the beta-barrel. cAMP- and cGMP-dependent protein kinases contain two tandem copies of the cyclic nucleotide-binding domain. The cAPK's are composed of two different subunits, a catalytic chain and a regulatory chain, which contains both copies of the domain. The cGPK's are single chain enzymes that include the two copies of the domain in their N-terminal section. Vertebrate cyclic nucleotide-gated ion-channels also contain this domain. Two such cations channels have been fully characterized, one is found in rod cells where it plays a role in visual signal transduction.
Denis Aristide Baylor is a Professor Emeritus of Neurobiology at Stanford University. He is known for his research on nerve cells in the retina of the eye. He developed a widely-used method for observing the electrical activity of single rod and cone photoreceptor cells and described how they encode light stimuli. Baylor’s work has been recognized by his election to the American Academy of Arts and Sciences, the National Academy of Sciences, and the Royal Society of London.
