title: Architecture of NarGH reveals a structural classification of Mo-bisMGD enzymes.
abstract: The structure of the catalytic and electron-transfer subunits (NarGH) of the integral membrane protein, respiratory nitrate reductase (Nar) has been determined to 2.0 A resolution revealing the molecular architecture of this Mo-bisMGD (molybdopterin-guanine-dinucleotide) containing enzyme which includes a previously undetected FeS cluster. Nar, together with the related enzyme formate dehydrogenase (Fdh-N), is a key enzyme in the generation of proton motive force across the membrane in Escherichia coli nitrate respiration. A comparative study revealed that Nar and Fdh-N employ different approaches for acquiring substrate, reflecting different catalytic mechanisms. Nar uses a very narrow and nonpolar substrate-conducting cavity with a nonspecific substrate binding site, whereas Fdh-N accommodates a wider, positively charged substrate-conducting cavity with a more specific substrate binding site. The Nar structure also demonstrates the first example of an Asp side chain acting as a Mo ligand providing a structural basis for the classification of Mo-bisMGD enzymes.
authors.affiliation: Division of Biomedical Sciences, Imperial College London, SW7 2AZ, UK.
authors.forename: Mika
authors.initials: M
authors.lastname: Jormakka
authors.forename: David
authors.initials: D
authors.lastname: Richardson
authors.forename: Bernadette
authors.initials: B
authors.lastname: Byrne
authors.forename: So
authors.initials: S
authors.lastname: Iwata
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D004579:Electron Transport / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology*; D005560:Formate Dehydrogenases / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000737:chemistry*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000737:chemistry*; D018892:Proton-Motive Force / Q000502:physiology; D055672:Static Electricity
chemical_list: D006639:Histidine; D008982:Molybdenum; D005560:Formate Dehydrogenases; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D003545:Cysteine