Photoreceptor protein

Photoreceptor proteins are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria. They mediate light responses as varied as visual perception, phototropism and phototaxis, as well as responses to light-dark cycles such as circadian rhythm and other photoperiodisms including control of flowering times in plants and mating seasons in animals.

Structure

Photoreceptor proteins typically consist of a protein attached to a non-protein chromophore (sometimes referred as photopigment, even so photopigment may also refer to the photoreceptor as a whole). The chromophore reacts to light via photoisomerization or photoreduction, thus initiating a change of the receptor protein which triggers a signal transduction cascade. Chromophores found in photoreceptors include retinal (retinylidene proteins, for example rhodopsin in animals),[1] flavin (flavoproteins, for example cryptochrome in plants and animals)[2] and bilin (biliproteins, for example phytochrome in plants).[3] The plant protein UVR8 is exceptional amongst photoreceptors in that it contains no external chromophore. Instead, UVR8 absorbs light through tryptophan residues within its protein coding sequence.[4]

Photoreceptors in animals

(Also see: Photoreceptor cell)

  • Melanopsin: in vertebrate retina, mediates pupillary reflex, involved in regulation of circadian rhythms
  • Photopsin: reception of various colors of light in the cone cells of vertebrate retina
  • Rhodopsin: green-blue light reception in the rod cells of vertebrate retina
  • Protein Kinase C: mediates photoreceptor deactivation, and retinal degeneration[5]
  • OPN5: sensitive to UV-light[6]

Photoreceptors in plants
  • UVR8: UV-B light reception
  • Cryptochrome: blue and UV-A light reception
  • Phototropin: blue and UV-A light perception (to mediate phototropism and chloroplast movement)
  • Zeitlupe: blue light entrainment of the circadian clock
  • Phytochrome: red and far-red light reception

All the photoreceptors listed above allow plants to sense light with wavelengths range from 280 nm (UV-B) to 750 nm (far-red light). Plants use light of different wavelengths as environmental cues to both alter their position and to trigger important developmental transitions.[7] The most prominent wavelength responsible for plant mechanisms is blue light, which can trigger cell elongation, plant orientation, and flowering.[8] One of the most important processes regulated by photoreceptors is known as photomorphogenesis. When a seed germinates underground in the absence of light, its stem rapidly elongates upwards. When it breaks through the surface of the soil, photoreceptors perceive light. The activated photoreceptors cause a change in developmental program; the plant starts producing chlorophyll and switches to photosynthetic growth.[9]

Photoreceptors in phototactic flagellates

(Also see: Eyespot apparatus)

  • Channelrhodopsin: in unicellular algae, mediates phototaxis
  • Chlamyopsin and volvoxopsin
  • Flavoproteins

Photoreceptors in archaea and bacteria
See also: Archaea and Bacteria
  • Bacteriophytochrome
  • sensory bacteriorhodopsin
  • Halorhodopsin
  • Proteorhodopsin
  • Cyanobacteriochrome

Photoreception and signal transduction

Responses to photoreception

See also
  • Biliproteins

References
  1. "Rhodopsin | biochemistry". Encyclopedia Britannica. Retrieved 2021-01-21.
  2. Lin, Chentao; Todo, Takeshi (2005-04-29). "The cryptochromes". Genome Biology. 6 (5): 220. doi:10.1186/gb-2005-6-5-220. ISSN 1474-760X. PMC 1175950. PMID 15892880.
  3. Rockwell, Nathan C.; Su, Yi-Shin; Lagarias, J. Clark (2006). "Phytochrome structure and signaling mechanisms". Annual Review of Plant Biology. 57: 837–858. doi:10.1146/annurev.arplant.56.032604.144208. ISSN 1543-5008. PMC 2664748. PMID 16669784.
  4. Li, Xiankun; Ren, Haisheng; Kundu, Mainak; Liu, Zheyun; Zhong, Frank W.; Wang, Lijuan; Gao, Jiali; Zhong, Dongping (2020-08-28). "A leap in quantum efficiency through light harvesting in photoreceptor UVR8". Nature Communications. 11 (1): 4316. Bibcode:2020NatCo..11.4316L. doi:10.1038/s41467-020-17838-6. ISSN 2041-1723. PMC 7455749. PMID 32859932.
  5. Smith, Dean P.; Ranganathan, Rama; Hardy, Robert W.; Marx, Julia; Tsuchida, Tammy; Zuker, Charles S. (1991). "Photoreceptor Deactivation and Retinal Degeneration Mediated by a Photoreceptor-Specific Protein Kinase C". Science. 254 (5037): 1478–1484. Bibcode:1991Sci...254.1478S. doi:10.1126/science.1962207. JSTOR 2879432. PMID 1962207. ProQuest 213560980.
  6. Kojima, Daisuke; Mori, Suguru; Torii, Masaki; Wada, Akimori; Morishita, Rika; Fukada, Yoshitaka (17 October 2011). "UV-Sensitive Photoreceptor Protein OPN5 in Humans and Mice". PLOS ONE. 6 (10): e26388. Bibcode:2011PLoSO...626388K. doi:10.1371/journal.pone.0026388. PMC 3197025. PMID 22043319.
  7. Galvão, Vinicius Costa; Fankhauser, Christian (October 2015). "Sensing the light environment in plants: photoreceptors and early signaling steps". Current Opinion in Neurobiology. 34: 46–53. doi:10.1016/j.conb.2015.01.013. PMID 25638281. S2CID 12390801.
  8. Christie, John M.; Briggs, Winslow R. (2001-04-13). "Blue Light Sensing in Higher Plants *". Journal of Biological Chemistry. 276 (15): 11457–11460. doi:10.1074/jbc.R100004200. ISSN 0021-9258. PMID 11279226.
  9. Briggs, Winslow R.; Olney, Margaret A. (1 January 2001). "Photoreceptors in Plant Photomorphogenesis to Date. Five Phytochromes, Two Cryptochromes, One Phototropin, and One Superchrome". Plant Physiology. 125 (1): 85–88. doi:10.1104/pp.125.1.85. PMC 1539332. PMID 11154303.
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