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Iron-sulfur clusters/semiquinones in complex I

T Ohnishi1

  • 1Johnson Research Foundation, Department of Biochemistry and Biophysics, and the University of Pennsylvania, Philadelphia, PA 19104, USA. ohnishi@mail.med.upenn.edu

Biochimica Et Biophysica Acta
|June 19, 1998
PubMed
Summary

Researchers studied NADH-quinone 1 oxidoreductase (Complex I) using bacterial models and EPR spectroscopy. They pinpointed the location of key redox centers and identified semiquinone species, advancing our understanding of this crucial enzyme.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • NADH-quinone 1 oxidoreductase (Complex I) is a vital energy-transducing enzyme in the mitochondrial respiratory chain.
  • Bovine heart Complex I is complex (43 subunits, ~1 million Da), while bacterial homologs offer simpler models (13-14 subunits).
  • Recent advances in bacterial genetics and spectroscopy have enabled detailed structural and functional analysis of Complex I.

Purpose of the Study:

  • To elucidate the structure-function relationships of Complex I's redox components.
  • To identify the precise locations of substrate binding sites, flavin, and iron-sulfur clusters.
  • To investigate the role and localization of semiquinone species in Complex I function.

Main Methods:

  • Comparative analysis of bacterial Complex I genes and protein structures.

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  • Site-directed mutagenesis and protein over-expression in bacterial systems.
  • Electron Paramagnetic Resonance (EPR) spectroscopy to detect and characterize redox centers and semiquinones.

    • Main Results:

    • The substrate (NADH) binding site, flavin, and most iron-sulfur clusters are located in the hydrophilic electron entry domain.
    • Cluster N2 is in the amphipathic domain, connecting the promontory and membrane regions.
    • Spin-spin interactions between Cluster N2 and two semiquinone species were observed, localizing them within the membrane.

    Conclusions:

    • Bacterial models provide powerful tools for dissecting Complex I structure and function.
    • The precise localization and ligation of iron-sulfur clusters, particularly N2, have been refined.
    • The study reveals the involvement and proximity of semiquinones to redox centers, offering insights into electron transfer mechanisms.