title: Structure of a novel farnesylated bilin from an insect--formation by α-cleavage of heme A of mitochondrial cytochrome c oxidases?
abstract: Biliproteins are present in almost all forms of life, and many of them play vital roles in photobiology. The bilin ligand of a recently characterized 500-kDa biliprotein from an insect has been isolated and its structure elucidated with chemical and spectroscopic techniques (UV-visible, IR, MS, NMR, and CD). This blue pigment, named CV-bilin, represents a unique high molecular mass derivative of biliverdin IXα, with an unusual 10E-configuration and a molecular mass of 852 Da, corresponding to C48H60N4O10. The high mass of this open-chain tetrapyrrole results from the presence of an epoxi-dihydroxyethylfarnesyl substituent at C-18 and a hydroxymethyl substituent at C-13. This substitution pattern exactly reflects that of heme A of mitochondrial cytochrome c oxidases with a hydroxyethylfarnesyl chain and a formyl group at corresponding positions of the cyclic tetrapyrrole. As no other natural product is known to show these structural features (heme O, the precursor of heme A, has a methyl group at C-13), this bilin is presumed to be derived from heme A by cleavage of the α-methine bridge and oxidative modifications at C-13 and the hydroxyethylfarnesyl chain. Possibly, a bilin structurally related to this insect bilin is also produced in other organisms as a result of mitochondrial turnover or degradation. As CV-bilin in complex with a specific protein is accumulated at the end of larval life, stored in the pupa, and finally transferred to the oocytes, a possible role of the free or protein-bound pigment in egg or embryonic development is discussed.
authors.affiliation: Institut für Allgemeine Zoologie und Endokrinologie, Universität Ulm, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Kayser
authors.forename: Victor
authors.initials: V
authors.lastname: Wray
authors.forename: Manfred
authors.initials: M
authors.lastname: Nimtz
mesh_terms: D000107:Acetylation; D000818:Animals; D001654:Bile Pigments / Q000737:chemistry* / Q000378:metabolism*; D001664:Biliverdine / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism*; D005260:Female; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D019476:Insect Proteins / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D015394:Molecular Structure; D009036:Moths / Q000254:growth & development / Q000378:metabolism; D054876:Prenylation; D013053:Spectrophotometry
chemical_list: D001654:Bile Pigments; D002352:Carrier Proteins; D019476:Insect Proteins; C053849:bilin-binding protein, insect; C027728:heme a; D006418:Heme; D003576:Electron Transport Complex IV; D001664:Biliverdine
keywords: bilins; heme A; insects; mitochondria; structure elucidation