The inner membrane of the mitochondrion folds inwards, forming the cristae. This folding allows a greater amount of membrane to be packed into the mitochondrion. The data in this study demonstrate that subunits e and g of the mitochondrial ATP synthase are involved in generating mitochondrial cristae morphology. These two subunits are non-essential components of ATP synthase and are required for the dimerization and oligomerization of ATP synthase. Mitochondria of yeast cells de®cient in either subunits e or g were found to have numerous digitations and onion-like structures that correspond to an uncontrolled biogenesis and/or folding of the inner mitochondrial membrane. The present data show that there is a link between dimerization of the mitochondrial ATP synthase and cristae morphology. A model is proposed of the assembly of ATP synthase dimers, taking into account the oligomerization of the yeast enzyme and earlier data on the ultrastructure of mitochondrial cristae, which suggests that the association of ATP synthase dimers is involved in the control of the biogenesis of the inner mitochondrial membrane. Keywords: ATP synthase oligomer/mitochondria/ morphology/yeast IntroductionThe mitochondrion is referred to as the`power house' of the cell, because it is responsible for the synthesis of the majority of ATP under aerobic conditions. The inner membrane of the mitochondrion contains the components of the electron transport chain. Oxidation/reduction reactions along the components of the electron transport chain generate a proton gradient that is used by ATP synthase to phosphorylate ADP, thereby producing ATP. To increase the capacity of the mitochondrion to synthesize ATP, the inner membrane is folded to form cristae. These folds allow a much greater amount of electron transport chain enzymes and ATP synthase to be packed into the mitochondrion. However, until now, little was known about how the inner membrane is able to form cristae. This study provides evidence that subunits of ATP synthase are involved in cristae formation.ATP synthase, or F 1 F 0 ATP synthase, is composed of a hydrophilic catalytic unit (F 1 ), which is located in the mitochondrial matrix, and a membranous domain (F 0 ), which anchors the enzyme in the inner mitochondrial membrane and mediates the conduction of protons that participate indirectly in ATP synthesis (Fillingame, 1999;Pedersen et al., 2000). Electron microscopy of negatively stained mitochondria revealed 9 nm diameter projections in the mitochondrial matrix (Ferna Ândez-Mora Ân, 1962), which were identi®ed as the hydrophilic catalytic units (F 1 ) of the F 1 F 0 ATP synthase (Racker et al., 1965). These projections were observed by electron microscopy to be arranged in a non-random, tightly ordered pattern on tubular cristae in Paramecium multimicronucleatum mitochondria using rapid techniques of freezing followed by fracturing, etching and replication (Allen et al., 1989). In this organism, the F 1 complexes are arranged as a double row of particles along the full length ...

Mitochondrial respiration relies on electron transport, an essential yet dangerous process in that it leads to the generation of reactive oxygen species (ROS). ROS can be neutralized within the mitochondria through enzymatic activity, yet the mechanism for steady-state removal of oxidized mitochondrial protein complexes and lipids is not well understood. We have previously characterized vesicular profiles budding from the mitochondria that carry selected cargo. At least one population of these mitochondria-derived vesicles (MDVs) targets the peroxisomes; however, the fate of the majority of MDVs was unclear. Here, we demonstrate that MDVs carry selected cargo to the lysosomes. Using a combination of confocal and electron microscopy, we observe MDVs in steady state and demonstrate that they are stimulated as an early response to oxidative stress, the extent of which is determined by the respiratory status of the mitochondria. Delivery to the lysosomes does not require mitochondrial depolarization and is independent of ATG5 and LC3, suggesting that vesicle delivery complements mitophagy. Consistent with this, ultrastructural analysis of MDV formation revealed Tom20-positive structures within the vesicles of multivesicular bodies. These data characterize a novel vesicle transport route between the mitochondria and lysosomes, providing insights into the basic mechanisms of mitochondrial quality control.

Mitochondrial dysfunction has long been associated with Parkinson's disease (PD). Parkin and PINK1, two genes associated with familial PD, have been implicated in the degradation of depolarized mitochondria via autophagy (mitophagy). Here, we describe the involvement of parkin and PINK1 in a vesicular pathway regulating mitochondrial quality control. This pathway is distinct from canonical mitophagy and is triggered by the generation of oxidative stress from within mitochondria. Wild-type but not PD-linked mutant parkin supports the biogenesis of a population of mitochondriaderived vesicles (MDVs), which bud off mitochondria and contain a specific repertoire of cargo proteins. These MDVs require PINK1 expression and ultimately target to lysosomes for degradation. We hypothesize that loss of this parkin-and PINK1-dependent trafficking mechanism impairs the ability of mitochondria to selectively degrade oxidized and damaged proteins leading, over time, to the mitochondrial dysfunction noted in PD.

Crista junctions (CJs) are important for mitochondrial organization and function, but the molecular basis of their formation and architecture is obscure. We have identified and characterized a mitochondrial membrane protein in yeast, Fcj1 (formation of CJ protein 1), which is specifically enriched in CJs. Cells lacking Fcj1 lack CJs, exhibit concentric stacks of inner membrane in the mitochondrial matrix, and show increased levels of F1FO–ATP synthase (F1FO) supercomplexes. Overexpression of Fcj1 leads to increased CJ formation, branching of cristae, enlargement of CJ diameter, and reduced levels of F1FO supercomplexes. Impairment of F1FO oligomer formation by deletion of its subunits e/g (Su e/g) causes CJ diameter enlargement and reduction of cristae tip numbers and promotes cristae branching. Fcj1 and Su e/g genetically interact. We propose a model in which the antagonism between Fcj1 and Su e/g locally modulates the F1FO oligomeric state, thereby controlling membrane curvature of cristae to generate CJs and cristae tips.