A novel cytosolic NADH:quinone oxidoreductase from Methanothermobacter marburgensis.

Eva Ullmann,Oliver Spadiut,Christina Divne,Christoph Herwig,Thomas Gundinger,Tien Chye Tan

doi:10.1042/bsr20140143

Eva Ullmann, Oliver Spadiut + Show 4 more

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https://doi.org/10.1042/bsr20140143

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Abstract

Methanothermobacter marburgensis is a strictly anaerobic, thermophilic methanogenic archaeon that uses methanogenesis to convert H2 and CO2 to energy. M. marburgensis is one of the best-studied methanogens, and all genes required for methanogenic metabolism have been identified. Nonetheless, the present study describes a gene (Gene ID 9704440) coding for a putative NAD(P)H:quinone oxidoreductase that has not yet been identified as part of the metabolic machinery. The gene product, MmNQO, was successfully expressed, purified and characterized biochemically, as well as structurally. MmNQO was identified as a flavin-dependent NADH:quinone oxidoreductase with the capacity to oxidize NADH in the presence of a wide range of electron acceptors, whereas NADPH was oxidized with only three acceptors. The 1.50 Å crystal structure of MmNQO features a homodimeric enzyme where each monomer comprises 196 residues folding into flavodoxin-like α/β domains with non-covalently bound FMN (flavin mononucleotide). The closest structural homologue is the modulator of drug activity B from Streptococcus mutans with 1.6 Å root-mean-square deviation on 161 Cα atoms and 28% amino-acid sequence identity. The low similarity at sequence and structural level suggests that MmNQO is unique among NADH:quinone oxidoreductases characterized to date. Based on preliminary bioreactor experiments, MmNQO could provide a useful tool to prevent overflow metabolism in applications that require cells with high energy demand.

Highlights

Aerobic cellular respiration in eukaryotes involves glycolysis, TCA cycle ( Krebs cycle or citric acid cycle) and respiratory chain
The function of MmNQO inferred from structural similarity leans towards an modulator of drug activity B (MdaB)-type activity, it should be emphasized that the overall sequence identity is low, and r.m.s.d. values high
Structural comparisons are insufficient to conclusively answer whether MmNQO prefers flavin mononucleotide (FMN) or FAD, and whether NADH or NADPH serves as coenzyme

Summary

INTRODUCTION

Aerobic cellular respiration in eukaryotes involves glycolysis, TCA (tricarboxylic acid) cycle ( Krebs cycle or citric acid cycle) and respiratory chain. Acetyl-CoA enters the TCA cycle within the mitochondrial matrix where oxidation occurs concomitantly with reduction of NAD + to NADH, and FAD to FADH2. The large quantities of NADH and FADH2 generated provide the high-potential reducing equivalents required for the ensuing electron-transfer events that build the PMF (proton motive force) necessary to power ATP synthesis through oxidative phosphorylation. This electron-transfer chain of inner mitochondrial-membrane protein complexes includes three proton pumps: NADH dehydrogenase (NADH:ubiqinone oxidoreductase; complex I [1]); cytochrome bc reductase (ubiquinol:cytochrom c oxidoreductase; complex III); and cytochrome c oxidase (complex IV).

Ullmann and others

RESULTS AND DISCUSSION

Conclusions