Eukaryotic Cell doi:10.1128/EC.00149-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Supramolecular organization of the respiratory chain in Neurospora crassa mitochondria
Isabel Marques,
Norbert A. Dencher,
Arnaldo Videira,
and
Frank Krause*
IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal; Physical Biochemistry, Department of Chemistry, Technische Universität Darmstadt, Petersenstrasse 22, D-64287 Darmstadt, Germany; ICBAS – Instituto de Ciências Biomédicas de Abel Salazar, Largo Prof. Abel Salazar 2, Universidade do Porto, 4050 Porto, Portugal
* To whom correspondence should be addressed. Email:
f_krause{at}pop.tu-darmstadt.de.
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Abstract |
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The existence of specific respiratory supercomplexes in mitochondria of most organisms has gained much momentum. However, its functional significance is still poorly understood. The availability of many deletion mutants in complex I (NADH:ubiquinone oxidoreductase) of Neurospora crassa, distinctly affected in the assembly process, offers unique opportunities to analyze the biogenesis of respiratory supercomplexes. Herein, we describe the role of complex I in assembly of respiratory complexes and supercomplexes as suggested by blue- and colorless-native PAGE and mass spectrometry analyzes of mildly solubilized mitochondria from both wild-type and eight deletion mutants. As an important refinement of the fungal respirasome model, we found that the standard respiratory chain of N. crassa comprises putative complex I dimers in addition to I-III-IV and III-IV-supercomplexes. Three Neurospora mutants able to assemble a complete complex I, only lacking the disrupted subunit, have respiratory supercomplexes, in particular I-III-IV-supercomplexes and complex I dimers, like the wild-type strain. Furthermore, we were able to detect the I-III-IV-supercomplexes in the nuo51 mutant with no overall enzymatic activity, representing the first example of inactive respirasomes. In addition, III-IV-supercomplexes were also present in strains lacking an assembled complex I, namely in four membrane arm subunit mutants as well as in the peripheral arm nuo30.4 mutant. In membrane arm mutants, high-molecular-weight species of the 30.4 kDa peripheral arm subunit comigrating with III-IV-supercomplexes and/or the prohibitin complex were detected. The data presented herein suggest that the biogenesis of complex I is linked with its assembly into supercomplexes.
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