title: Biosynthesis of hexahydroxyperylenequinone melanin via oxidative aryl coupling by cytochrome P-450 in Streptomyces griseus.
abstract: Dihydroxyphenylalanine (DOPA) melanins formed from tyrosine by tyrosinases are found in microorganisms, plants, and animals. Most species in the soil-dwelling, gram-positive bacterial genus Streptomyces produce DOPA melanins and melanogenesis is one of the characteristics used for taxonomy. Here we report a novel melanin biosynthetic pathway involving a type III polyketide synthase (PKS), RppA, and a cytochrome P-450 enzyme, P-450mel, in Streptomyces griseus. In vitro reconstitution of the P-450mel catalyst with spinach ferredoxin-NADP(+) reductase/ferredoxin revealed that it catalyzed oxidative biaryl coupling of 1,3,6,8-tetrahydroxynaphthalene (THN), which was formed from five molecules of malonyl-coenzyme A by the action of RppA to yield 1,4,6,7,9,12-hexahydroxyperylene-3,10-quinone (HPQ). HPQ readily autopolymerized to generate HPQ melanin. Disruption of either the chromosomal rppA or P-450mel gene resulted in abolishment of the HPQ melanin synthesis in S. griseus and a decrease in the resistance of spores to UV-light irradiation. These findings show that THN-derived melanins are not exclusive in eukaryotic fungal genera but an analogous pathway is conserved in prokaryotic streptomycete species as well. A vivid contrast in THN melanin biosynthesis between streptomycetes and fungi is that the THN synthesized by the action of a type III PKS is used directly for condensation in the former, while the THN synthesized by the action of type I PKSs is first reduced and the resultant 1,8-dihydroxynaphthalene is then condensed in the latter.
authors.affiliation: Department of Biotechnology, Graduate School of Agriculture and Life Sciences, University of Tokyo, Japan.
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Funa
authors.forename: Masanori
authors.initials: M
authors.lastname: Funabashi
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ohnishi
authors.forename: Sueharu
authors.initials: S
authors.lastname: Horinouchi
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000096:biosynthesis; D017353:Gene Deletion; D008543:Melanins / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D009284:Naphthols / Q000737:chemistry / Q000378:metabolism; D010569:Perylene / Q000031:analogs & derivatives*; D013171:Spores, Bacterial / Q000528:radiation effects; D013305:Streptomyces griseus / Q000378:metabolism* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: C121288:1,3,6,8-tetrahydroxynaphthalene; D008543:Melanins; D009284:Naphthols; C506456:hexahydroxyperylenequinone melanin; D010569:Perylene; D004295:Dihydroxyphenylalanine; C040616:DOPA melanin; D003577:Cytochrome P-450 Enzyme System; D000217:Acyltransferases; C020141:flavanone synthetase