The Redox-Bohr Group Associated with Iron-Sulfur Cluster N2 of Complex I

Klaus Zwicker,Alexander Galkin,Stefan Dröse,Ljuban Grgic,Stefan Kerscher,Ulrich Brandt

doi:10.1074/jbc.m603442200

Klaus Zwicker, Alexander Galkin + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m603442200

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Abstract

Proton pumping respiratory complex I (NADH:ubiquinone oxidoreductase) is a major component of the oxidative phosphorylation system in mitochondria and many bacteria. In mammalian cells it provides 40% of the proton motive force needed to make ATP. Defects in this giant and most complicated membrane-bound enzyme cause numerous human disorders. Yet the mechanism of complex I is still elusive. A group exhibiting redox-linked protonation that is associated with iron-sulfur cluster N2 of complex I has been proposed to act as a central component of the proton pumping machinery. Here we show that a histidine in the 49-kDa subunit that resides near iron-sulfur cluster N2 confers this redox-Bohr effect. Mutating this residue to methionine in complex I from Yarrowia lipolytica resulted in a marked shift of the redox midpoint potential of iron-sulfur cluster N2 to the negative and abolished the redox-Bohr effect. However, the mutation did not significantly affect the catalytic activity of complex I and protons were pumped with an unchanged stoichiometry of 4 H(+)/2e(-). This finding has significant implications on the discussion about possible proton pumping mechanism for complex I.

Highlights

In mammalian cells mitochondrial complex I (NADH: ubiquinone oxidoreductase) provides 40% of the proton motive force needed to make ATP
The x-ray structure of the peripheral arm of complex I from Thermus thermophilus has been solved [3]. It is still unclear how complex I couples electron transfer from NADH to ubiquinone with the vectorial translocation of four protons across the bioenergetic membrane [4, 5]
The structural model for the ubiquinone reducing catalytic core of complex I [1, 16] that had been deduced from distinct homologies between [NiFe] hydrogenase and complex I [17, 18] was confirmed by the structure of the peripheral arm of complex I [3]

Summary

Introduction

In mammalian cells mitochondrial complex I (NADH: ubiquinone oxidoreductase) provides 40% of the proton motive force needed to make ATP. A group exhibiting redox-linked protonation that is associated with iron-sulfur cluster N2 of complex I has been proposed to act as a central component of the proton pumping machinery.

Results

Conclusion