title: Crystal structure of the nitrogenase-like dark operative protochlorophyllide oxidoreductase catalytic complex (ChlN/ChlB)2.
abstract: During (bacterio)chlorophyll biosynthesis of many photosynthetically active organisms, dark operative protochlorophyllide oxidoreductase (DPOR) catalyzes the two-electron reduction of ring D of protochlorophyllide to form chlorophyllide. DPOR is composed of the subunits ChlL, ChlN, and ChlB. Homodimeric ChlL(2) bearing an intersubunit [4Fe-4S] cluster is an ATP-dependent reductase transferring single electrons to the heterotetrameric (ChlN/ChlB)(2) complex. The latter contains two intersubunit [4Fe-4S] clusters and two protochlorophyllide binding sites, respectively. Here we present the crystal structure of the catalytic (ChlN/ChlB)(2) complex of DPOR from the cyanobacterium Thermosynechococcus elongatus at a resolution of 2.4 A. Subunits ChlN and ChlB exhibit a related architecture of three subdomains each built around a central, parallel beta-sheet surrounded by alpha-helices. The (ChlN/ChlB)(2) crystal structure reveals a [4Fe-4S] cluster coordinated by an aspartate oxygen alongside three cysteine ligands. Two equivalent substrate binding sites enriched in aromatic residues for protochlorophyllide substrate binding are located at the interface of each ChlN/ChlB half-tetramer. The complete octameric (ChlN/ChlB)(2)(ChlL(2))(2) complex of DPOR was modeled based on the crystal structure and earlier functional studies. The electron transfer pathway via the various redox centers of DPOR to the substrate is proposed.
authors.affiliation: Institut für Mikrobiologie, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany.
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Bröcker
authors.affiliation: Institut für Mikrobiologie, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schomburg
authors.affiliation: Division of Structural Biology, Helmholtz-Centre for Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany.
authors.forename: Dirk W
authors.initials: DW
authors.lastname: Heinz
authors.affiliation: Institut für Mikrobiologie, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Jahn
authors.affiliation: Division of Structural Biology, Helmholtz-Centre for Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany; Department of Biotechnology, University of the Western Cape, Private Bag X17, Bellville 7535, Cape Town, South Africa. Electronic address: wschubert@uwc.ac.za.
authors.forename: Wolf-Dieter
authors.initials: WD
authors.lastname: Schubert
authors.affiliation: Institut für Mikrobiologie, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Moser
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000201:enzymology*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008958:Models, Molecular; D009591:Nitrogenase / Q000737:chemistry; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry*; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011521:Protochlorophyllide; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D011521:Protochlorophyllide; D009591:Nitrogenase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase