title: Discovery of the first light-dependent protochlorophyllide oxidoreductase in anoxygenic phototrophic bacteria.
abstract: In all photosynthetic organisms, chlorophylls function as light-absorbing photopigments allowing the efficient harvesting of light energy. Chlorophyll biosynthesis recurs in similar ways in anoxygenic phototrophic proteobacteria as well as oxygenic phototrophic cyanobacteria and plants. Here, the biocatalytic conversion of protochlorophyllide to chlorophyllide is catalysed by evolutionary and structurally distinct protochlorophyllide reductases (PORs) in anoxygenic and oxygenic phototrophs. It is commonly assumed that anoxygenic phototrophs only contain oxygen-sensitive dark-operative PORs (DPORs), which catalyse protochlorophyllide reduction independent of the presence of light. In contrast, oxygenic phototrophs additionally (or exclusively) possess oxygen-insensitive but light-dependent PORs (LPORs). Based on this observation it was suggested that light-dependent protochlorophyllide reduction first emerged as a consequence of increased atmospheric oxygen levels caused by oxygenic photosynthesis in cyanobacteria. Here, we provide experimental evidence for the presence of an LPOR in the anoxygenic phototrophic α-proteobacterium Dinoroseobacter shibae DFL12(T). In vitro and in vivo functional assays unequivocally prove light-dependent protochlorophyllide reduction by this enzyme and reveal that LPORs are not restricted to cyanobacteria and plants. Sequence-based phylogenetic analyses reconcile our findings with current hypotheses about the evolution of LPORs by suggesting that the light-dependent enzyme of D. shibae DFL12(T) might have been obtained from cyanobacteria by horizontal gene transfer.
authors.affiliation: Institut für Molekulare Enzymtechnologie, Heinrich-Heine-Universität Düsseldorf, Forschungszentrum Jülich, Wilhelm-Johnen Straße, D-52428, Jülich, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Kaschner
authors.forename: Anita
authors.initials: A
authors.lastname: Loeschcke
authors.forename: Judith
authors.initials: J
authors.lastname: Krause
authors.forename: Bui Quang
authors.initials: BQ
authors.lastname: Minh
authors.forename: Achim
authors.initials: A
authors.lastname: Heck
authors.forename: Stephan
authors.initials: S
authors.lastname: Endres
authors.forename: Vera
authors.initials: V
authors.lastname: Svensson
authors.forename: Astrid
authors.initials: A
authors.lastname: Wirtz
authors.forename: Arndt
authors.initials: A
authors.lastname: von Haeseler
authors.forename: Karl-Erich
authors.initials: KE
authors.lastname: Jaeger
authors.forename: Thomas
authors.initials: T
authors.lastname: Drepper
authors.forename: Ulrich
authors.initials: U
authors.lastname: Krauss
mesh_terms: D020561:Alphaproteobacteria / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis / Q000528:radiation effects; D008027:Light; D008969:Molecular Sequence Data; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D052817:Phototrophic Processes / Q000528:radiation effects; D010802:Phylogeny; D011521:Protochlorophyllide / Q000378:metabolism; D016415:Sequence Alignment; D014908:Triticum / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D011521:Protochlorophyllide; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D010100:Oxygen