title: Catalytic importance of acidic amino acids on subunit NuoB of the Escherichia coli NADH:ubiquinone oxidoreductase (complex I).
abstract: The NADH:ubiquinone oxidoreductase (complex I) from Escherichia coli is composed of 13 subunits called NuoA through NuoN and contains one FMN and 9 iron-sulfur clusters as redox groups. Electron transfer from NADH to ubiquinone is coupled with the translocation of protons across the membrane by a yet unknown mechanism. Redox-induced Fourier transform infrared difference spectroscopy showed that the oxidation of iron-sulfur cluster N2 located on NuoB is accompanied by the protonation of acidic amino acid(s). Here, we describe the effect of mutating the conserved acidic amino acids on NuoB. The complex was assembled in all mutants but the electron transfer activity was completely abolished in the mutants E67Q, D77N, and D94N. The complex isolated from these mutants contained N2 although in diminished amounts. The protonation of acidic amino acid(s) coupled with the oxidation of N2 was not detectable in the complex from the mutant E67Q. However, the conservative mutations E67D and D77E did not disturb the enzymatic activity, and the signals because of the protonation of acidic amino acid(s) were detectable in the E67D mutant. We discuss the possible participation of Glu(67) in a proton pathway coupled with the redox reaction of N2.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Flemming
authors.forename: Petra
authors.initials: P
authors.lastname: Hellwig
authors.forename: Simone
authors.initials: S
authors.lastname: Lepper
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Kloer
authors.forename: Thorsten
authors.initials: T
authors.lastname: Friedrich
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D004578:Electron Spin Resonance Spectroscopy; D042967:Electron Transport Complex I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D016415:Sequence Alignment
chemical_list: D029968:Escherichia coli Proteins; C480162:NuoB protein, E coli; D042967:Electron Transport Complex I