Bilin (biochemistry)

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Bilirubin, a yellow bilin, is a breakdown product of heme Bilirubin ZZ.png
Bilirubin, a yellow bilin, is a breakdown product of heme

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.

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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.

Examples of bilins are found in animals (cardinal examples are bilirubin and biliverdin), 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]

Bilin-binding protein in butterfly wings

Butterfly wings are a new site of porphyrin synthesis and cleavage where bilin is portrayed; the expression of the lipocalin bilin-binding protein in Pieris brassicae. [4] The function of the biliprotein during wing development is still unknown, as is the existence of an active pathway for porphyrin synthesis and cleavage in insect wings, which has been demonstrated here for the first time. The bilin-binding protein from Pieris brassicae, which was discovered to have a crystal structure, was one of the initial members of the lipocalins protein superfamily, which has since grown significantly. It is a blue pigment protein that can be clearly identified by its amino acid sequence and crystal structure. The bilin-binding protein is predominantly present in hemolymph, fat body, and epidermis in the last instar larval and in the wings of the adult insect of Pieris brassicae. [5] Although it has recently been discovered that three swallowtail butterfly larval color patterns are correlated with the combination of bilin-binding protein and the yellow-related gene, additional physiological activities are still unknown. [6] Normally, insect bilins are joined to proteins to create a variety of biliproteins that have been identified in Lepidoptera and other insects. The presence of the blue and yellow pigments contributes to the blue-green hue of some lepidopteran larvae. Blue pigments and yellow carotenoids are thought to work together as camouflage. [7]

Bilin-binding protein is a member of the lipocalin family, which includes extracellular proteins with a number of molecular ligand features in common, including the ability to bind tiny, primarily lipophilic compounds like retinol. [8] Members of the lipocalin family have mostly been classified as transport proteins, but it is clear that they also perform a range of other tasks, including retinol transport, invertebrate cryptic coloring, olfaction, and pheromone transmission. There is a lot of structural and functional variation in the lipocalin family, both within and between species.

See also

Related Research Articles

<span class="mw-page-title-main">Chlorophyll</span> Green pigments found in plants, algae and bacteria

Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words χλωρός, khloros and φύλλον, phyllon ("leaf"). Chlorophyll allow plants to absorb energy from light.

<span class="mw-page-title-main">Heme</span> Chemical coordination complex of an iron ion chelated to a porphyrin

Heme, or haem, is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver.

<span class="mw-page-title-main">Stercobilin</span> Chemical compound

Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism. It is the chemical responsible for the brown color of human feces and was originally isolated from feces in 1932. Stercobilin can be used as a marker for biochemical identification of fecal pollution levels in rivers.

Phycobilins are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Most of their molecules consist of a chromophore which makes them coloured. They are unique among the photosynthetic pigments in that they are bonded to certain water-soluble proteins, known as phycobiliproteins. Phycobiliproteins then pass the light energy to chlorophylls for photosynthesis.

<span class="mw-page-title-main">Aminolevulinic acid</span> Endogenous non-proteinogenic amino acid

δ-Aminolevulinic acid, an endogenous non-proteinogenic amino acid, is the first compound in the porphyrin synthesis pathway, the pathway that leads to heme in mammals, as well as chlorophyll in plants.

<span class="mw-page-title-main">Aminolevulinic acid synthase</span> Class of enzymes

Aminolevulinic acid synthase (ALA synthase, ALAS, or delta-aminolevulinic acid synthase) is an enzyme (EC 2.3.1.37) that catalyzes the synthesis of δ-aminolevulinic acid (ALA) the first common precursor in the biosynthesis of all tetrapyrroles such as hemes, cobalamins and chlorophylls. The reaction is as follows:

In molecular biology, biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. This process often consists of metabolic pathways. Some of these biosynthetic pathways are located within a single cellular organelle, while others involve enzymes that are located within multiple cellular organelles. Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides. Biosynthesis is usually synonymous with anabolism.

<span class="mw-page-title-main">Biliverdin</span> Chemical compound

Biliverdin is a green tetrapyrrolic bile pigment, and is a product of heme catabolism. It is the pigment responsible for a greenish color sometimes seen in bruises.

<span class="mw-page-title-main">Heme oxygenase</span>

Heme oxygenase, or haem oxygenase, is an enzyme that catalyzes the degradation of heme to produce biliverdin, ferrous ion, and carbon monoxide.

<span class="mw-page-title-main">Hydroxymethylbilane</span> Chemical compound

Hydroxymethylbilane, also known as preuroporphyrinogen, is an organic compound that occurs in living organisms during the synthesis of porphyrins, a group of critical substances that include haemoglobin, myoglobin, and chlorophyll. The name is often abbreviated as HMB.

<span class="mw-page-title-main">Biological pigment</span> Substances produced by living organisms

Biological pigments, also known simply as pigments or biochromes, are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments. Many biological structures, such as skin, eyes, feathers, fur and hair contain pigments such as melanin in specialized cells called chromatophores. In some species, pigments accrue over very long periods during an individual's lifespan.

<span class="mw-page-title-main">Lipocalin</span>

The lipocalins are a family of proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids, and most lipocalins are also able to bind to complexed iron as well as heme. They share limited regions of sequence homology and a common tertiary structure architecture. This is an eight stranded antiparallel beta barrel with a repeated + 1 topology enclosing an internal ligand binding site.

<span class="mw-page-title-main">Protoporphyrin IX</span> Chemical compound

Protoporphyrin IX is an organic compound, classified as a porphyrin, that plays an important role in living organisms as a precursor to other critical compounds like heme (hemoglobin) and chlorophyll. It is a deeply colored solid that is not soluble in water. The name is often abbreviated as PPIX.

Odorant-binding proteins (OBPs) are small soluble proteins secreted by auxiliary cells surrounding olfactory receptor neurons, including the nasal mucus of many vertebrate species and in the sensillar lymph of chemosensory sensilla of insects. OBPs are characterized by a specific protein domain that comprises six α-helices joined by three disulfide bonds. Although the function of the OBPs as a whole is not well established, it is believed that they act as odorant transporters, delivering the odorant molecules to olfactory receptors in the cell membrane of sensory neurons.

In organic chemistry, bilane is a compound with the formula C19H20N4 or [(C4H4N)−CH2−(C4H3N)−]2CH2. It is a tetrapyrrole, a class of compounds with four independent pyrrole rings. Specifically, the molecule can be described as four pyrrole molecules C4H5N connected in an open chain by three methylene bridges −CH2 at carbons adjacent to the nitrogens, replacing the respective hydrogens.

15,16-dihydrobiliverdin:ferredoxin oxidoreductase is an enzyme that catalyzes the following chemical reaction

<span class="mw-page-title-main">Bilirubin oxidase</span>

In enzymology, a bilirubin oxidase, BOD or BOx, (EC 1.3.3.5) is an enzyme encoded by a gene in various organisms that catalyzes the chemical reaction

Chemosensory proteins (CSPs) are small soluble proteins which mediate olfactory recognition at the periphery of sensory receptors in insects, similarly to odorant-binding proteins. The typical structure of CSPs is made of six or seven α-helical chains of about 110-120 amino acids, including four cysteines that build two small loops, two adjacent disulfide bridges, and a globular "prism-like" functional structure [5]. Three CSP structures have been solved in moths and locusts [5-8].

<span class="mw-page-title-main">Chlorophyllide</span> Chemical compound

Chlorophyllide a and Chlorophyllide b are the biosynthetic precursors of chlorophyll a and chlorophyll b respectively. Their propionic acid groups are converted to phytyl esters by the enzyme chlorophyll synthase in the final step of the pathway. Thus the main interest in these chemical compounds has been in the study of chlorophyll biosynthesis in plants, algae and cyanobacteria. Chlorophyllide a is also an intermediate in the biosynthesis of bacteriochlorophylls.

<span class="mw-page-title-main">Biliprotein</span>

Biliproteins are pigment protein compounds that are located in photosynthesising organisms such as algae and certain insects. They refer to any protein that contains a bilin chromophore. In plants and algae, the main function of biliproteins is to make the process of light accumulation required for photosynthesis more efficient; while in insects they play a role in growth and development. Some of their properties: including light-receptivity, light-harvesting and fluorescence have made them suitable for applications in bioimaging and as indicators; while other properties such as anti-oxidation, anti-aging and anti-inflammation in phycobiliproteins have given them potential for use in medicine, cosmetics and food technology. While research on biliproteins dates back as far as 1950, it was hindered due to issues regarding biliprotein structure, lack of methods available for isolating individual biliprotein components, as well as limited information on lyase reactions . Research on biliproteins has also been primarily focused on phycobiliproteins; but advances in technology and methodology, along with the discovery of different types of lyases, has renewed interest in biliprotein research, allowing new opportunities for investigating biliprotein processes such as assembly/disassembly and protein folding.

References

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