Melanopsin

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Melanopsin
Properties of human protein
Mass / length primary structure 478 amino acids
Secondary to quaternary structure multipass membrane receptor
Identifier
Gene name OPN4
External IDs
Occurrence
Homology family Opsin-4
Parent taxon Vertebrates

Melanopsin , also called OPN4 , is a protein of the opsin family that binds retinal as a chromophore and thus becomes a light-sensitive molecule, a photopigment. It was first identified in 1998 in the clawed frog ( Xenopus laevis ). In this animal, it is found in the melanocytes of the skin, eyes and brain . In mammals such as mice and humans, melanopsin was found in special nerve cells in the eye, where it is used to register the brightness of the surroundings.

Melanopsin signals

The signals from these neurons also intrinsically photosensitive ganglion cells ( intrinsically photosensitive retinal ganglion cells ; ipRGCs) called, contribute to the synchronization of the circadian rhythm with the natural day-night cycle and the social day-night rhythm. In addition, these signals also control the production of the hormone s melatonin in the evening and at night, as well as the size of the pupil by the pupillary reflex .

The photosensitive ganglion cells represent a subgroup of the retinal ganglion cells (RGCs) in the retina and become light-sensitive due to the melanopsin that is formed. Via axons that go directly to the suprachiasmatic nuclei (SCN) of the hypothalamus , they send sustained, brightness-reflecting signals that are interpreted as timers for clock signals of endogenous rhythms. Studies have shown in particular the importance of melanopsin for the light-dependent suppression of melatonin secretion in the epiphysis , and thus its connection with the tasks of the internal clock . In humans, only a small proportion of the retinal ganglion cells (around 1%) contain melanopsin.

Spectral sensitivity

Melanopsin has a broad spectral sensitivity, with a maximum at around 480 nm. The spectral brightness perception in the photopic range , which is based on the L and M cone cells of the eye containing the photopsins , has a different course (see V lambda curve ) . Since 2018, the spectral sensitivities for the photoreceptors in the human retina have been available in standardized form by the International Commission on Illumination (CIE). This also means that the strength of the melanopsin activation, for example in lighting planning, cannot be determined by conventional photometers .

Individual evidence

  1. ↑ UniProt Q9UHM6
  2. ↑ Provencio I, Jiang G, De Grip WJ, Hayes WP, Rollag MD: Melanopsin: An opsin in melanophores, brain, and eye . In: Proceedings of the National Academy of Sciences of the United States of America . 95, No. 1, January 1998, pp. 340-5. doi : 10.1073 / pnas.95.1.340 . PMID 9419377 . PMC 18217 (free full text).
  3. ↑ Abhishek S. Prayag, Raymond P. Najjar, Claude Gronfier: Melatonin suppression is exquisitely sensitive to light and primarily driven by melanopsin in humans . In: Journal of Pineal Research . tape 66 , no. 4 , May 2019, ISSN  0742-3098 , p. e12562 , doi : 10.1111 / jpi.12562 ( wiley.com [accessed January 27, 2020]).
  4. ↑ Manuel Spitschan: Photoreceptor inputs to pupil control . In: Journal of Vision . tape 19 , no. 9 , August 15, 2019, ISSN  1534-7362 , p. 5 , doi : 10.1167 / 19.9.5 , PMID 31415056 , PMC 6699792 (free full text) - ( arvojournals.org [accessed January 27, 2020]).
  5. ^ Nasir-Ahmad S, Lee SCS, Martin PR, Grünert U: Melanopsin-expressing ganglion cells in human retina: Morphology, distribution, and synaptic connections . In: J Comp Neurol . 527, No. 1, January 2019, pp. 312-327. doi : 10.1002 / cne.24176 . PMID 28097654 .
  6. ↑ Bailes HJ, Lucas RJ: Human melanopsin forms a pigment maximally sensitive to blue light (λmax ≈ 479 nm) supporting activation of G (q / 11) and G (i / o) signaling cascades . In: Proceedings of the Royal Society B: Biological Sciences . 280, No. 1759, May 2013, p. 20122987. doi : 10.1098 / rspb.2012.2987 . PMID 23554393 . PMC 3619500 (free full text).
  7. ^ CIE System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light . International Commission on Illumination, December 12, 2018, doi : 10.25039 / s026.2018 .

Web links

Wiktionary: Melanopsin  - explanations of meanings, word origins, synonyms, translations