Human F1F0 ATP Synthase, Mitochondrial Ultrastructure and OXPHOS Impairment: A (Super-)Complex Matter?

Abstract

Mitochondrial morphogenesis is a key process of cell physiology. It is essential for the proper function of this double membrane-delimited organelle, as it ensures the packing of the inner membrane in a very ordered pattern called cristae. In yeast, the mitochondrial ATP synthase is able to form dimers that can assemble into oligomers. Two subunits (e and g) are involved in this supramolecular organization. Deletion of the genes encoding these subunits has no effect on the ATP synthase monomer assembly or activity and only affects its dimerization and oligomerization. Concomitantly, the absence of subunits e and g and thus, of ATP synthase supercomplexes, promotes the modification of mitochondrial ultrastructure suggesting that ATP synthase oligomerization is involved in cristae morphogenesis. We report here that in mammalian cells in culture, the shRNA-mediated down-regulation of subunits e and g affects the stability of ATP synthase and results in a 50% decrease of the available functional enzyme. Comparable to what was shown in yeast, when subunits e and g expression are repressed, ATP synthase dimers and oligomers are less abundant when assayed by native electrophoresis. Unexpectedly, mammalian ATP synthase dimerization/oligomerization impairment has functional consequences on the respiratory chain leading to a decrease in OXPHOS activity. Finally these structural and functional alterations of the ATP synthase have a strong impact on the organelle itself leading to the fission of the mitochondrial network and the disorganization of mitochondrial ultrastructure. Unlike what was shown in yeast, the impairment of the ATP synthase oligomerization process drastically affects mitochondrial ATP production. Thus we propose that mutations or deletions of genes encoding subunits e and g may have physiopathological implications.

Structure and function of the intermembrane space domain of mammalian FoF1ATP synthase

“…forms b-e-g complex present in early DDM/column extracts in absence of lipids [28] cryo-EM [16] null-mutants and cryo-EM studies of yeast enzyme [8,20] knock-down in human enzyme [10] cross-linking [29,30], [present study] assembly study [31] f low tight association with Fo retained in IMD and Fo kink-less subcomplex structures in yeast vicinity to b, A6L, e, g and 6.8PL…”

“…Furthermore, biochemical and structural data indicate that subunits e and g are indispensable for membrane bending of mitochondrial ATP synthase [8,10,32]. For example, the absence of subunits e and g in a recent cryo-EM study of monomeric yeast F o F 1 ATP resulted in a structure lacking the membrane-bending F o kink [25].…”

“…N-terminus exposed to matrix present in early DDM/column extracts in absence of lipids [28] cryo-EM [20] cross-linking [29,30] proteolysis [29] g low tight association with Fo retained in IMD less cryo-EM structure exhibiting Fo kink thought to cause membrane bending (Fo kink) in neighborhood to b, e, f N-terminus exposed to matrix forms b-e-g complex present in early DDM/column extracts in absence of lipids [28] cryo-EM [16] null-mutants and cryo-EM studies of yeast enzyme [8,20] knock-down in human enzyme [10] cross-linking [29], [present study]…”

“…To fulfill its energy transforming function, it utilizes the proton motive force (pmf) generated by the electron transport chain to recycle ATP from ADP+Pi via proton flow fueled rotary catalysis [1][2][3][4][5][6]. Moreover, mitochondrial ATP synthase plays an essential role in membrane bending and cristae formation [7][8][9][10][11]. Fragility and flexibility of this large membrane protein complex (>600 kDa, 17 different subunits) pose a major challenge for purification and structure determination of the entire complex.…”

Bacterial Electron Transfer Chains Primed by Proteomics

“…However, such a short distance is less apparent for the quinone binding sites of complexes I and III (Dudkina, Eubel, Keegstra, Boekema, & Braun, 2005), and quinone was shown to move freely through the mitochondrial inner membrane during respiration (Blaza, Serreli, Jones, Mohammed, & Hirst, 2014;Lenaz & Genova, 2009;Trouillard, Meunier, & Rappaport, 2011). Another possibility is that individual complexes cooperatively assist and stabilise each other's assemblies during SC formation and maintenance (Calvaruso et al, 2012;Chojnacka, Gornicka, Oeljeklaus, Warscheid, & Chacinska, 2015;Cui, Conte, Fox, Zara, & Winge, 2014;Duarte & Videira, 2009;Habersetzer et al, 2013;Marques, Dencher, Videira, & Krause, 2007;Stroh et al, 2004;see however: Maas, Krause, Dencher, & Sainsard-Chanet, 2009). Indeed, deletion or mutation of factors known to be involved in the assembly of one complex affected assembly of other complexes as well and of SCs as a whole.…”