{{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 431787953 | Name = | ImageFile = Scytonemin.png | ImageSize = 200 | ImageAlt = | PIN = (3''E'',3′''E'')-3,3′-Bis[(4-hydroxyphenyl)methylidene][1,1′-bi(cyclopropa[''b'']indole)]-2,2′(3''H'',3′''H'')-dione | OtherNames = Scytonemin | SystematicName = | Section1 = {{Chembox Identifiers | CASNo_Ref = {{cascite|correct|??}} | CASNo = 152075-98-4 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = VPQ7YG2DMW | PubChem = 135473381 | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 505177 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 16736974 | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 90127 | SMILES = C1=CC=C2N=C\3C(=C(C(=O)/C3=C/C4=CC=C(C=C4)O)C5=C6C(=NC7=CC=CC=C67)/C(=C\C8=CC=C(C=C8)O)/C5=O)C2=C1 | InChI = 1/C36H20N2O4/c39-21-13-9-19(10-14-21)17-25-33-29(23-5-1-3-7-27(23)37-33)31(35(25)41)32-30-24-6-2-4-8-28(24)38-34(30)26(36(32)42)18-20-11-15-22(40)16-12-20/h1-18,39-40H/b25-17+,26-18+ | InChIKey = CGZKSPLDUIRCIO-RPCRKUJJBK | StdInChI_Ref = {{stdinchicite|changed|chemspider}} | StdInChI = 1S/C36H20N2O4/c39-21-13-9-19(10-14-21)17-25-33-29(23-5-1-3-7-27(23)37-33)31(35(25)41)32-30-24-6-2-4-8-28(24)38-34(30)26(36(32)42)18-20-11-15-22(40)16-12-20/h1-18,39-40H/b25-17+,26-18+ | StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} | StdInChIKey = CGZKSPLDUIRCIO-RPCRKUJJSA-N}} | Section2 = {{Chembox Properties | Formula = C<sub>36</sub>H<sub>20</sub>N<sub>2</sub>O<sub>4</sub> | MolarMass = 544.6 g/mol | MolarMass_notes = | Appearance = brown solid | Density = | MeltingPt = | MeltingPt_notes = | BoilingPt = | BoilingPt_notes = | SublimationConditions = | Solubility = | SolubilityProduct = | SolubilityProductAs = | Solvent = | pKa = | pKb = | IsoelectricPt = | LambdaMax = 370nm | Absorbance = | BandGap = | ElectronMobility = | SpecRotation = | MagSus = | ThermalConductivity = | RefractIndex = | Viscosity = | Dipole = | SolubleOther = 25mg/ml DMSO }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} | Section4 = | Section5 = | Section6 = }} '''Scytonemin''' is a secondary metabolite and an extracellular matrix (sheath) pigment synthesized by many strains of cyanobacteria, including ''Nostoc'', ''Scytonema'', ''Calothrix'', ''Lyngbya'', ''Rivularia'', ''Chlorogloeopsis'', and ''Hyella''.<ref>{{Cite journal|last=Sinha, Hader|date=2008-03-01|title=UV-protectants in cyanobacteria|journal=Plant Science|volume=174|issue=3|pages=278–289|doi=10.1016/j.plantsci.2007.12.004|issn=0168-9452}}</ref> Scytonemin-synthesizing cyanobacteria often inhabit highly insolated terrestrial, freshwater and coastal environments such as deserts, semideserts, rocks, cliffs, marine intertidal flats, and hot springs.<ref>{{Cite book|url=https://www.springer.com/us/book/9789400738546|title=Ecology of Cyanobacteria II - Their Diversity in Space and {{!}} Brian A. Whitton {{!}} Springer|language=en|isbn=978-94-007-3854-6|publisher=Springer|year=2012}}</ref>
The pigment was originally discovered in 1849 by Swiss botanist Carl Nägeli,<ref>{{Cite book|url=https://archive.org/details/gattungeneinzell00ng|title=Gattungen einzelliger Algen physiologisch und systematisch bearbeitet|last=Nägeli|first=Carl|date=1849|publisher=Zürich, Friedrich Schulthess|others=MBLWHOI Library}}</ref> although the structure remained unsolved until 1993.<ref name="pmid8405307">{{cite journal |pages=825–9 |doi=10.1007/BF01923559 |title=The structure of scytonemin, an ultraviolet sunscreen pigment from the sheaths of cyanobacteria |year=1993 |last1=Proteau |first1=P. J. |last2=Gerwick |first2=W. H. |last3=Garcia-Pichel |first3=F. |last4=Castenholz |first4=R. |journal=Experientia |volume=49 |issue=9 |pmid=8405307|s2cid=22975257 }}</ref> It is an aromatic indole alkaloid built from two identical condensation products of tryptophan<nowiki/>yl- and tyrosy<nowiki/>l-derived subunits linked through a carbon-carbon bond.<ref name="pmid8405307" /> Depending on the redox conditions it can exist in two inter-convertible forms: a more common oxidized yellow-brown form which is insoluble in water and only slightly soluble in organic solvents, such as pyridine, and a reduced form with bright red color that is more soluble in organic solvents.<ref>{{Cite journal|last1=Garcia-Pichel|first1=Ferran|last2=Castenholz|first2=Richard W.|date=1991-06-01|title=Characterization and Biological Implications of Scytonemin, a Cyanobacterial Sheath Pigment1|journal=Journal of Phycology|language=en|volume=27|issue=3|pages=395–409|doi=10.1111/j.0022-3646.1991.00395.x|bibcode=1991JPcgy..27..395G |s2cid=84058783|issn=1529-8817}}</ref> Scytonemin absorbs very strongly and very broadly across the UV-C-UV-B-UV-A-violet-blue spectral region, with an in vivo maximum absorption at 370 nm and an in vitro maximum absorption at 386 and 252 nm, and with smaller peaks at 212, 278 and 300 nm.<ref>{{Cite journal|last1=Sinha|first1=Rajeshwar|last2=Klisch|first2=M|last3=Vaishampayan|first3=Akhouri|last4=Häder|first4=Donat|date=1999-11-01|title=Biochemical and spectroscopic characterization of the cyanobacterium Lyngbya sp. inhabiting mango (Mangifera indica) trees: Presence of an ultraviolet-absorbing pigment, scytonemin|url=https://www.researchgate.net/publication/266383468|journal=Acta Protozoologica|volume=38|pages=291–298}}</ref>
It is believed that scytonemin acts as a highly efficient protective biomolecule (sunscreen) that filters out damaging high frequency UV rays while at the same time allowing the transmittance of wavelengths necessary for photosynthesis.<ref>{{Cite journal|last1=Ekebergh|first1=Andreas|last2=Sandin|first2=Peter|last3=Mårtensson|first3=Jerker|date=2015-11-25|title=On the photostability of scytonemin, analogues thereof and their monomeric counterparts|journal=Photochemical & Photobiological Sciences|language=en|volume=14|issue=12|doi=10.1039/C5PP00215J|pmid=26452010|issn=1474-9092|pages=2179–2186|s2cid=23558706 }}</ref> Its biosynthesis in cyanobacteria is mostly triggered by exposure to UV-A and UV-B wavelengths.<ref>{{Cite journal|last1=Sorrels|first1=Carla M.|last2=Proteau|first2=Philip J.|last3=Gerwick|first3=William H.|date=2009-07-15|title=Organization, Evolution, and Expression Analysis of the Biosynthetic Gene Cluster for Scytonemin, a Cyanobacterial UV-Absorbing Pigment|journal=Applied and Environmental Microbiology|language=en|volume=75|issue=14|pages=4861–4869|doi=10.1128/AEM.02508-08|issn=0099-2240|pmid=19482954|pmc=2708446|bibcode=2009ApEnM..75.4861S }}</ref><ref>{{Cite journal|last1=Rastogi|first1=Rajesh P.|last2=Incharoensakdi|first2=Aran|date=2014-01-01|title=Characterization of UV-screening compounds, mycosporine-like amino acids, and scytonemin in the cyanobacteriumLyngbyasp. CU2555|journal=FEMS Microbiology Ecology|language=en|volume=87|issue=1|pages=244–256|doi=10.1111/1574-6941.12220|pmid=24111939|issn=0168-6496|doi-access=free|bibcode=2014FEMME..87..244R }}</ref>
Recently, Couradeau and coworkers found that cyanobacterial soil crusts warm the soil surface by as much as 10 °C through the production and accumulation of scytonemin pigments.<ref>{{Cite journal|last1=Couradeau|first1=Estelle|last2=Karaoz|first2=Ulas|last3=Lim|first3=Hsiao Chien|last4=Rocha|first4=Ulisses Nunes da|last5=Northen|first5=Trent|last6=Brodie|first6=Eoin|last7=Garcia-Pichel|first7=Ferran|date=2016-01-20|title=Bacteria increase arid-land soil surface temperature through the production of sunscreens|journal=Nature Communications|language=En|volume=7|article-number=10373|doi=10.1038/ncomms10373|pmid=26785770|pmc=4735820|bibcode=2016NatCo...710373C}}</ref> This effect is due to the dissipation of the absorbed photons by the scytonemin molecules into heat.
== Biosynthesis == The biosynthesis in ''Lyngbya aestuarii'' was recently explored by Balskus, Case, and Walsh. It proceeds by the conversion of L-tryptophan to 3-indole pyruvic acid, followed by coupling to ''p''-hydroxyphenylpyruvic acid. Cyclization of the resultant β-ketoacid yields a tricyclic ketone. Oxidation and dimerization yields the completed natural product. Three scytonemin biosynthetic enzymes are necessary, denoted as ScyA-C.<ref name="pmid21501195">{{cite journal|last1=Balskus|first1=Emily P.|last2=Case|first2=Rebecca J.|last3=Walsh|first3=Christopher T.|year=2011|title=The biosynthesis of cyanobacterial sunscreen scytonemin in intertidal microbial mat communities|journal=FEMS Microbiology Ecology|volume=77|issue=2|pages=1–11|doi=10.1111/j.1574-6941.2011.01113.x|pmid=21501195|url=https://dash.harvard.edu/bitstream/handle/1/12169551/nihms292647.pdf?sequence=1|pmc=3134115|bibcode=2011FEMME..77..322B }}</ref>
880x880px|center|Scytonemin biosynthesis in ''Lyngbya aestuarii''.<ref name="pmid21501195" />
== References == <references />
Category:Biological pigments Category:Secondary metabolites Category:Cyanobacteria