Bilin (biochemistry)

Bilins, bilanes or bile pigments are biological pigments formed in many organisms as a metabolic product of certain porphyrins. Bilin (also called bilichrome) was named as a bile pigment of mammals, but can also be found in lower vertebrates, invertebrates, as well as red algae, green plants and cyanobacteria. Bilins can range in color from red, orange, yellow or brown to blue or green.

Bilirubin, a yellow bilin, is a breakdown product of heme

In chemical terms, bilins are linear arrangements of four pyrrole rings (tetrapyrroles). In human metabolism, bilirubin is a breakdown product of heme. A modified bilane is an intermediate in the biosynthesis and uroporphyrinogen III from porphobilinogen (PBG).

Examples of bilins are found in animals, and phycocyanobilin, the chromophore of the photosynthetic pigment phycocyanin in algae and plants. In plants, bilins also serve as the photopigments of the photoreceptor protein phytochrome. An example of an invertebrate bilin is micromatabilin, which is responsible for the green color of the Green Huntsman Spider, Micrommata virescens.[1]

In plants

Most photosynthetic, oxygen-producing organisms contain the positive chlorophyll biosynthesis regulator GENOMES UNCOUPLED 4 (GUN4). Research suggests that GUN4 regulates chlorophyll synthesis, by activating the enzyme Magnesium chelatase, which catalyzes the insertion of Mg2+ into Protoporphyrin IX.[2] Bilins noncovalently bind to CrGUN4, an algal GUN4 from Chlamydomonas reinhardtii, which has been shown to participate in retrograde signaling.[3]

See also

References
  1. Oxford GS, Gillespie RG (1998). "Evolution and ecology of spider coloration". Annual Review of Entomology. 43: 619–43. doi:10.1146/annurev.ento.43.1.619. PMID 15012400.
  2. Richter AS, Hochheuser C, Fufezan C, Heinze L, Kuhnert F, Grimm B (November 2016). "Phosphorylation of GENOMES UNCOUPLED 4 Alters Stimulation of Mg Chelatase Activity in Angiosperms". Plant Physiology. 172 (3): 1578–1595. doi:10.1104/pp.16.01036. PMC 5100749. PMID 27688621.
  3. Hu JH, Chang JW, Xu T, Wang J, Wang X, Lin R, et al. (October 2021). "Structural basis of bilin binding by the chlorophyll biosynthesis regulator GUN4". Protein Science. 30 (10): 2083–2091. doi:10.1002/pro.4164. PMC 8442963. PMID 34382282.
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