The diheme cytochrome b subunit (Narl) of Escherichia coli nitrate reductase A (NarGHI): structure, function, and interaction with quinols.
Significant recent advances have been made in studies of the major dissimilatory nitrate reductase (NarGHI) of Escherichia coli. This enzyme is a complex iron-sulfur ([Fe-S]) molybdoenzyme that oxidizes menaquinol or ubiquinol at a periplasmically oriented Q-site (Qp site), and reduces nitrate at a cytoplasmically-oriented molybdo-(bismolybdopterin guanine dinucleotide) (Mo-bisMGD) cofactor. The Qp site, as well as two hemes, termed bL and bH, are localized in a hydrophobic diheme cytochrome b(Narl) that: (i) provides a conduit for electron-transfer from the periplasmically-oriented Qp-site; (ii) provides a membrane anchoring functionality for the membrane-extrinsic subunits (NarGH) that coordinate the Mo-bisMGD (NarG) and four [Fe-S] clusters (NarH); and (iii) helps ensure the separation of sites of H+-yielding and H+-consuming reactions such that enzyme turnover leads to the generation of a proton-electrochemical potential across the cytoplasmic membrane. This minireview focuses on recent advances and future prospects for the diheme cytochrome b subunit (Narl) of NarGHI.
Rothery
R A
RA
MRC Group in the Molecular Biology of Membrane Proteins, Department of Biochemistry, University of Alberta, Edmonton, Canada.
Blasco
F
F
Magalon
A
A
Weiner
J H
JH
D000595:Amino Acid Sequence; D003573:Cytochrome b Group / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D006150:Guanine Nucleotides / Q000378:metabolism; D006418:Heme / Q000378:metabolism; D006873:Hydroquinones / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009942:Organometallic Compounds / Q000378:metabolism; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D003573:Cytochrome b Group; D006150:Guanine Nucleotides; D006873:Hydroquinones; D009942:Organometallic Compounds; D021122:Protein Subunits; C106961:bis(molybdopterin guanine dinucleotide)molybdenum; D006418:Heme; D008982:Molybdenum; D009565:Nitrate Reductases; D050901:Nitrate Reductase