title: Two Unrelated 8-Vinyl Reductases Ensure Production of Mature Chlorophylls in Acaryochloris marina.
abstract: The major photopigment of the cyanobacterium Acaryochloris marina is chlorophyll d, while its direct biosynthetic precursor, chlorophyll a, is also present in the cell. These pigments, along with the majority of chlorophylls utilized by oxygenic phototrophs, carry an ethyl group at the C-8 position of the molecule, having undergone reduction of a vinyl group during biosynthesis. Two unrelated classes of 8-vinyl reductase involved in the biosynthesis of chlorophylls are known to exist, BciA and BciB. The genome of Acaryochloris marina contains open reading frames (ORFs) encoding proteins displaying high sequence similarity to BciA or BciB, although they are annotated as genes involved in transcriptional control (nmrA) and methanogenesis (frhB), respectively. These genes were introduced into an 8-vinyl chlorophyll a-producing ΔbciB strain of Synechocystis sp. strain PCC 6803, and both were shown to restore synthesis of the pigment with an ethyl group at C-8, demonstrating their activities as 8-vinyl reductases. We propose that nmrA and frhB be reassigned as bciA and bciB, respectively; transcript and proteomic analysis of Acaryochloris marina reveal that both bciA and bciB are expressed and their encoded proteins are present in the cell, possibly in order to ensure that all synthesized chlorophyll pigment carries an ethyl group at C-8. Potential reasons for the presence of two 8-vinyl reductases in this strain, which is unique for cyanobacteria, are discussed.
  
  
  OBJECTIVE
  The cyanobacterium Acaryochloris marina is the best-studied phototrophic organism that uses chlorophyll d for photosynthesis. Unique among cyanobacteria sequenced to date, its genome contains ORFs encoding two unrelated enzymes that catalyze the reduction of the C-8 vinyl group of a precursor molecule to an ethyl group. Carrying a reduced C-8 group may be of particular importance to organisms containing chlorophyll d Plant genomes also contain orthologs of both of these genes; thus, the bacterial progenitor of the chloroplast may also have contained both bciA and bciB.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Guangyu E
authors.initials: GE
authors.lastname: Chen
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Andrew
authors.initials: A
authors.lastname: Hitchcock
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Jackson
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Roy R
authors.initials: RR
authors.lastname: Chaudhuri
authors.affiliation: ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Dickman
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom dpc5323@psu.edu.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Canniffe
mesh_terms: D002734:Chlorophyll / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics*; D009154:Mutation; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics* / Q000378:metabolism*; D010788:Photosynthesis; D010802:Phylogeny; D040901:Proteomics; D046939:Synechocystis / Q000235:genetics
chemical_list: D002734:Chlorophyll; C107509:chlorophyll d; D044925:Oxidoreductases Acting on CH-CH Group Donors