Macromolecular organization of ATP synthase and complex I in whole mitochondria

Abstract

We used electron cryotomography to study the molecular arrangement of large respiratory chain complexes in mitochondria from bovine heart, potato, and three types of fungi. Long rows of ATP synthase dimers were observed in intact mitochondria and cristae membrane fragments of all species that were examined. The dimer rows were found exclusively on tightly curved cristae edges. The distance between dimers along the rows varied, but within the dimer the distance between F 1 heads was constant. The angle between monomers in the dimer was 70°or above. Complex I appeared as L-shaped densities in tomograms of reconstituted proteoliposomes. Similar densities were observed in flat membrane regions of mitochondrial membranes from all species except Saccharomyces cerevisiae and identified as complex I by quantumdot labeling. The arrangement of respiratory chain proton pumps on flat cristae membranes and ATP synthase dimer rows along cristae edges was conserved in all species investigated. We propose that the supramolecular organization of respiratory chain complexes as proton sources and ATP synthase rows as proton sinks in the mitochondrial cristae ensures optimal conditions for efficient ATP synthesis.cryoelectron tomography | subtomogram averaging | membrane curvature | membrane potential | mitochondrial ultrastructure M itochondria, the powerhouses of eukaryotic cells, generate ATP, the universal energy carrier in all life forms. The F 1 F o ATP synthase uses the energy stored in the electrochemical proton gradient across the inner mitochondrial membrane to produce ATP from ADP and phosphate. The proton gradient is established by the respiratory chain complexes I, III, and IV, which pump protons out of the mitochondrial matrix into the cristae space while transferring electrons from the electron donors NADH, FADH, or succinate (via complex II) to the final electron acceptor O 2 . The F 1 F o ATP synthase and complex I (NADH dehydrogenase) are the largest membrane protein complexes in mitochondria, composed of more than 20 or 40 individual protein subunits, respectively (1, 2). The 600-kDa ATP synthase consists of the F o part in the membrane that works like a proton-driven turbine, and the catalytic F 1 part on the matrix side. The two parts are held together by a static peripheral stalk and a rotating central stalk that transmits the torque from the rotor unit in the membrane to the catalytic F 1 head (3, 4). Complex I is an L-shaped molecule of approximately 1 MDa. Its membrane arm has three or four proton-pumping modules, while the matrix arm catalyzes electron transfer from NADH to the hydrophobic electron acceptor ubiquinol (5). The structures of both complexes have been determined by X-ray crystallography, either partially in the case of the F 1 F o ATP synthase (6), or at low resolution in the case of mitochondrial complex I (7, 8), but their relative organization in the mitochondrial inner membrane is largely unknown.The two large complexes occur at an approximate ratio of one molecule of complex I per 3.5 ATP...

Structure of the yeast F 1 F o -ATP synthase dimer and its role in shaping the mitochondrial cristae

“…Tomograms of mitochondrial membranes from the yeast Saccharomyces cerevisiae were assessed for the distribution of ATP synthase, which appears as 10 nm spherical densities positioned 5 nm above the membrane (5,6). Pairs of particles along highly curved membrane ridges were extracted and averaged.…”

“…The mitochondrial ATP synthase is located in the inner membrane cristae (1,2), where it forms dimers (3). These dimers are organized in rows, located along the highly curved ridges of the cristae (4)(5)(6). The ATP synthase of yeast (Saccharomyces cerevisiae) has a molecular mass of approximately 600 kDa and consists of thirteen different core subunits (α 3 , β 3 , γ, δ, ε, OSCP, 4, 6, 8, 9 10 , d, f , and h) (7).…”

Disrupted in schizophrenia 1 (DISC1) is a constituent of the mammalian mitochondrial contact site and cristae organizing system (MICOS) complex, and is essential for oxidative phosphorylation

“…Cristae increase the membrane area available for OXPHOS and play an important role in the organization of ATP synthases dimers, which have been linked to more proficient ATP synthesis (42)(43)(44)(45). Destructured MICOS caused by DISC1 knockdown ends up causing OXPHOS disassembly and dysfunction, with the consequent bioenergetics deficit (Fig.…”

Mitofilin complexes: conserved organizers of mitochondrial membrane architecture

“…Cristae membranes are enriched in respiratory chain complexes, F 1 F o -ATP synthase, ADP/ ATP carrier and Oxa1, a protein required for biogenesis of mitochondrially encoded subunits of respiratory chain complexes (Figure 1) (Gilkerson et al , 2003 ;Vogel et al , 2006 ;Wurm and Jakobs , 2006 ;Stoldt et al , 2012 ). These membrane regions are the main sites of ATP production in mitochondria (Gilkerson et al , 2003 ;Strauss et al , 2008 ;Davies et al , 2011 ). In contrast, the inner boundary membrane mainly contains protein complexes that are involved in the functional cooperation between inner and outer mitochondrial membranes, like the machineries for the import of nuclear-encoded mitochondrial precursor proteins (Figure 1) (Vogel et al , 2006 ;Wurm and Jakobs , 2006 ).…”

“…Mitochondrial architecture is important for crucial mitochondrial functions, including ATP generation via oxidative phosphorylation (OXPHOS), calcium homeostasis and programmed cell death (apoptosis) (Frey and Mannella , 2000 ;Frezza et al , 2006 ;Clapham , 2007 ;Strauss et al , 2008 ;Rizzuto et al , 2009 ;Martins de Brito and Scorrano , 2010 ;Davies et al , 2011 ;Green et al , 2011 ). Accordingly, alterations of mitochondrial morphology are a hallmark of numerous human diseases, ranging from myopathies, neuropathies and neurodegenerative disorders to metabolic diseases and different types of cancer.…”