Supramolecular Organization of the Respiratory Chain in Neurospora crassa Mitochondria

Abstract

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 polyacrylamide gel electrophoresis and mass spectrometry analyses of mildly solubilized mitochondria from the 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, lacking only 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-mass 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.

Protein Network of the Pseudomonas aeruginosa Denitrification Apparatus

“…Model for a nitrate respirasome of P. aeruginosa. Currently, respirasome research-the investigation of megacomplexes involved in respiration-focuses almost exclusively on the mitochondrial electron transport chain of eukaryotes (3)(4)(5)(6)(7)(8)(9)(10). Here, we describe a highly structured, well-organized membrane-attached protein-protein network in bacteria involved in anaerobic energy generation (Fig.…”

“…In contrast, much less is known about the dynamic interactions of these protein complexes in the respiratory chains. For humans (3), cattle (4), mice (5), spinach (6), potatoes (7), and yeast species (8,9), the existence of supracomplexes has been proposed and proven. Similarly, membrane-localized multienzyme complexes were investigated in great detail for bacterial and plant photosyn-thesis (10)(11)(12).…”

“…The periplasmic nitrite reductase NirS catalyzes the next reaction as follows: NO 2 Ϫ ϩ 2H ϩ ϩ e Ϫ ¡ NO ϩ H 2 O. The P. aeruginosa enzyme is a cytochrome cd 1 carrying an electron-receiving heme c and a catalytic site with heme d 1 (3,8-dioxo-17-acrylate-porphyrindione) (22)(23)(24). The two c-type cytochromes NirM and NirC act as electron donors (25).…”

Supramolecular organizations in the aerobic respiratory chain of Escherichia coli

“…In eukaryotes, supercomplexes formed by complexes I, III and IV, the so-called respirasomes, have been observed in mitochondria of bovine heart [8e10], mouse liver [11], potato tuber [12,13], Neurospora crassa [14] and Yarrowia lipolytica [15]. Associations of complexes III and IV have also been described in these organisms, as well as in Saccharomyces cerevisiae, that lacks complex I, and for which a mitochondrial dehydrogenase supercomplex has been proposed [16].…”

Novel Insights into the Role of Neurospora crassa NDUFAF2, an Evolutionarily Conserved Mitochondrial Complex I Assembly Factor

“…These supercomplexes are regarded as relevant for reducing the diffusion distance of the substrates, improving electron transfer, reducing the formation of reactive oxygen species, and stabilizing the individual respiratory complexes (3)(4)(5)(6).…”