title: Roles of subunit NuoK (ND4L) in the energy-transducing mechanism of Escherichia coli NDH-1 (NADH:quinone oxidoreductase).
abstract: The bacterial H(+)-translocating NADH:quinone oxidoreductase (NDH-1) catalyzes electron transfer from NADH to quinone coupled with proton pumping across the cytoplasmic membrane. The NuoK subunit (counterpart of the mitochondrial ND4L subunit) is one of the seven hydrophobic subunits in the membrane domain and bears three transmembrane segments (TM1-3). Two glutamic residues located in the adjacent transmembrane helices of NuoK are important for the energy coupled activity of NDH-1. In particular, mutation of the highly conserved carboxyl residue ((K)Glu-36 in TM2) to Ala led to a complete loss of the NDH-1 activities. Mutation of the second conserved carboxyl residue ((K)Glu-72 in TM3) moderately reduced the activities. To clarify the contribution of NuoK to the mechanism of proton translocation, we relocated these two conserved residues. When we shifted (K)Glu-36 along TM2 to positions 32, 38, 39, and 40, the mutants largely retained energy transducing NDH-1 activities. According to the recent structural information, these positions are located in the vicinity of (K)Glu-36, present in the same helix phase, in an immediately before and after helix turn. In an earlier study, a double mutation of two arginine residues located in a short cytoplasmic loop between TM1 and TM2 (loop-1) showed a drastic effect on energy transducing activities. Therefore, the importance of this cytosolic loop of NuoK ((K)Arg-25, (K)Arg-26, and (K)Asn-27) for the energy transducing activities was extensively studied. The probable roles of subunit NuoK in the energy transducing mechanism of NDH-1 are discussed.
authors.affiliation: Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Jesus
authors.initials: J
authors.lastname: Torres-Bacete
authors.forename: Prem Kumar
authors.initials: PK
authors.lastname: Sinha
authors.forename: Motoaki
authors.initials: M
authors.lastname: Sato
authors.forename: Gaurav
authors.initials: G
authors.lastname: Patki
authors.forename: Mou-Chieh
authors.initials: MC
authors.lastname: Kao
authors.forename: Akemi
authors.initials: A
authors.lastname: Matsuno-Yagi
authors.forename: Takao
authors.initials: T
authors.lastname: Yagi
mesh_terms: D000595:Amino Acid Sequence; D004734:Energy Metabolism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009243:NAD / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D063347:Native Polyacrylamide Gel Electrophoresis; D010084:Oxidation-Reduction; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D011522:Protons
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D050505:Mutant Proteins; C098483:NADH dehydrogenase subunit 4; C540656:NuoH protein, E coli; D021122:Protein Subunits; D011522:Protons; D009243:NAD; D018698:Glutamic Acid; D009245:NADH Dehydrogenase