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Torres-Bacete, J, Nakamaru-Ogiso, E, Matsuno-Yagi, A and Yagi, T (2007) Characterization of the NuoM (ND4) subunit in Escherichia coli NDH-1: conserved charged residues essential for energy-coupled activities. J. Biol. Chem. 282:36914-22


The proton-translocating NADH-quinone (Q) oxidoreductase (NDH-1) from Escherichia coli is composed of two segments: a peripheral arm and a membrane arm. The membrane arm contains 7 hydrophobic subunits. Of these subunits, NuoM, a homolog of the mitochondrial ND4 subunit, is proposed to be involved in proton translocation and Q-binding. Therefore, we conducted site-directed mutation of 15 amino acid residues of NuoM and investigated their properties. In all mutants, the assembly of the whole enzyme seemed intact. Mutation of highly conserved Glu144 and Lys234 leads to almost total elimination of energy-transducing NDH-1 activities as well as increased production of superoxide radicals. Their NADH dehydrogenase activities were almost normal. Because these two residues are predicted to be located in the transmembrane segments of NuoM, the results strongly suggest that they participate in proton translocation. Although it is hypothesized that His interacts with a Q head group, mutations at four His moderately inhibited NDH-1 activities and had almost no effect on the Km values for Q or IC50 values of capsaicin-40, a competitive inhibitor for the Q binding site. The data suggest that these His are not involved in the catalytic Q-binding. Functional roles of NuoM and advantages of NDH-1 research as a model for mitochondrial complex I study have been discussed.


PubMed Online version:10.1074/jbc.M707855200


Binding Sites/physiology; Capsaicin/pharmacology; Catalytic Domain/genetics; Cell Membrane/enzymology; Cell Membrane/genetics; Electron Transport Complex I/genetics; Electron Transport Complex I/metabolism; Energy Metabolism/drug effects; Energy Metabolism/physiology; Escherichia coli/enzymology; Escherichia coli/genetics; Escherichia coli Proteins/genetics; Escherichia coli Proteins/metabolism; Hydrophobic and Hydrophilic Interactions; Ion Transport/drug effects; Ion Transport/physiology; Mutagenesis, Site-Directed; NADH Dehydrogenase/genetics; NADH Dehydrogenase/metabolism; Protein Binding/drug effects; Protein Binding/physiology; Protons; Sensory System Agents/pharmacology; Ubiquinone/genetics; Ubiquinone/metabolism



Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status


Contributes to

GO:0003954: NADH dehydrogenase activity



Figure 4

I used the Contributes to qualifier because, NuoM KO "...lacked a fully assembled NDH-1" showing NuoM is a subunit that is important in the assembly of NDH-1.(1st paragraph under figure 4 in column 2) Without NuoM, the NADH dehydrogenase activity of the complex is inhibited reinforcing the notion that this subunit contributes that activity of the complex. I did not use the NADH (ubiquinone) dehydrogenase activity GO because this paper does not have experimental evidence supporting that.



GO:0015992: proton transport



Figure 6. Proton gradient was measured using ACMA. They looked at membrane vesicles which had the NDH1 complex containing normal NuoM and mutant NuoM subunits. The vesicles that contained unmutated were able to create a proton gradient where as those that had NuoM knocked out were not suggesting that NuoM is a major factor in the proton translocation process. It is IMP because this was determined by comparing mutant phenotypes of NuoM.



GO:0045838: positive regulation of membrane potential



Figure 5. Membrane vesicles were made containing NDH1 complexs with normal NuoM and mutated NuoM subunits. Membrane potential was measured by changes of oxonol VI. With NuoM, a change in membrane potential was seen but when it was knocked out, there was no change in membrane potential. This suggests NuoM is essential in the complex in order to stimulate membrane potential changes.


See also


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