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Functional dissection of the proton pumping modules of mitochondrial complex I
Stefan Dröse1, Stephanie Krack, Lucie Sokolova
1Molecular Bioenergetics Group, Medical School, Cluster of Excellence Frankfurt Macromolecular Complexes, Center for Membrane Proteomics, Johann Wolfgang Goethe-Universität, Frankfurt, Germany.
Plos Biology
|September 3, 2011
Summary
Mitochondrial complex I proton pumping involves two distinct modules in its membrane arm. Deleting an accessory subunit in Yarrowia complex I revealed these modules and their function in proton transport.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Mitochondrial complex I is crucial for cellular respiration, transferring electrons and pumping protons.
- Defects in complex I are linked to human degenerative diseases.
- X-ray crystallography revealed complex I's structure, but the proton pumping mechanism remains unclear.
Purpose of the Study:
- To investigate the molecular mechanism of proton pumping in mitochondrial complex I.
- To identify the specific subunits responsible for proton translocation.
- To understand the role of accessory subunits in complex I function.
Main Methods:
- Single particle analysis of a modified Yarrowia complex I subcomplex (nb8mΔ).
- Proteomic analysis of holo and subcomplex subunit composition.
- Biochemical assays to measure proton pumping activity.
Main Results:
- A subcomplex (nb8mΔ) lacking part of the membrane domain was generated by deleting an accessory subunit gene.
- Two candidate proton-pump subunits (ND4 and ND5) were absent in nb8mΔ.
- nb8mΔ retained partial proton pumping activity, albeit at half the stoichiometry of the complete enzyme.
Conclusions:
- The membrane arm of mitochondrial complex I contains at least two functionally distinct proton pump modules.
- These modules are likely connected in series via a helical transmission element.
- Accessory subunits play a role in the complete assembly and function of the proton pump modules.
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