Rcf proteins and their differential specificity for respiratory chain complexes: A unique role for Rcf2 on oxygen sensitive supercomplexes?

The respiratory chain, embedded in the inner mitochondrial membrane, is organized as a network of individual complexes, as well as large supercomplex structures. In the yeast S. cerevisiae, these supercomplexes consist of a dimeric cytochrome bc-complex adjoined by one or two copies of cytochrome c oxidase.

Defining the architecture of the human TIM22 complex by chemical crosslinking.

The majority of mitochondrial proteins are nuclear encoded and imported into mitochondria as precursor proteins via dedicated translocases. The translocase of the inner membrane 22 (TIM22) is a multisubunit molecular machine specialized for the translocation of hydrophobic, multi-transmembrane-spanning proteins with internal targeting signals into the inner mitochondrial membrane. Here, we undertook a crosslinking-mass spectrometry (XL-MS) approach to determine the molecular arrangement of subunits of the human TIM22 complex.

MICOS assembly controls mitochondrial inner membrane remodeling and crista junction redistribution to mediate cristae formation.

Mitochondrial function is critically dependent on the folding of the mitochondrial inner membrane into cristae; indeed, numerous human diseases are associated with aberrant crista morphologies. With the MICOS complex, OPA1 and the F F -ATP synthase, key players of cristae biogenesis have been identified, yet their interplay is poorly understood. Harnessing super-resolution light and 3D electron microscopy, we dissect the roles of these proteins in the formation of cristae in human mitochondria.

A Cross-linking Mass Spectrometry Approach Defines Protein Interactions in Yeast Mitochondria.

Protein cross-linking and the analysis of cross-linked peptides by mass spectrometry is currently receiving much attention. Not only is this approach applied to isolated complexes to provide information about spatial arrangements of proteins, but it is also increasingly applied to entire cells and their organelles. As in quantitative proteomics, the application of isotopic labeling further makes it possible to monitor quantitative changes in the protein-protein interactions between different states of a system.

COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.

The mitochondrial cytochrome c oxidase, the terminal enzyme of the respiratory chain, contains heme and copper centers for electron transfer. The conserved COX2 subunit contains the Cu site, a binuclear copper center. The copper chaperones SCO1, SCO2, and COA6, are required for Cu center formation.

A MICOS-TIM22 Association Promotes Carrier Import into Human Mitochondria.

Mitochondrial membrane proteins with internal targeting signals are inserted into the inner membrane by the carrier translocase (TIM22 complex). For this, precursors have to be initially directed from the TOM complex in the outer mitochondrial membrane across the intermembrane space toward the TIM22 complex. How these two translocation processes are topologically coordinated is still unresolved.

Inhibition of proteasome rescues a pathogenic variant of respiratory chain assembly factor COA7.

Nuclear and mitochondrial genome mutations lead to various mitochondrial diseases, many of which affect the mitochondrial respiratory chain. The proteome of the intermembrane space (IMS) of mitochondria consists of several important assembly factors that participate in the biogenesis of mitochondrial respiratory chain complexes. The present study comprehensively analyzed a recently identified IMS protein cytochrome oxidase assembly factor 7 (COA7), or RESpiratory chain Assembly 1 (RESA1) factor that is associated with a rare form of mitochondrial leukoencephalopathy and complex IV deficiency.

Overlapping Role of Respiratory Supercomplex Factor Rcf2 and Its N-terminal Homolog Rcf3 in Saccharomyces cerevisiae.

The mitochondrial electron transport chain consists of individual protein complexes arranged into large macromolecular structures, termed respiratory chain supercomplexes or respirasomes. In the yeast Saccharomyces cerevisiae, respiratory chain supercomplexes form by association of the bc complex with the cytochrome c oxidase. Formation and maintenance of these assemblies are promoted by specific respiratory supercomplex factors, the Rcf proteins.

Cox26 is a novel stoichiometric subunit of the yeast cytochrome c oxidase.

The cytochrome c oxidase (COX) is the terminal enzyme of the respiratory chain. The complex accepts electrons from cytochrome c and passes them onto molecular oxygen. This process contributes to energy capture in the form of a membrane potential across the inner membrane.

Protein cofactor competition regulates the action of a multifunctional RNA helicase in different pathways.

A rapidly increasing number of RNA helicases are implicated in several distinct cellular processes, however, the modes of regulation of multifunctional RNA helicases and their recruitment to different target complexes have remained unknown. Here, we show that the distribution of the multifunctional DEAH-box RNA helicase Prp43 between its diverse cellular functions can be regulated by the interplay of its G-patch protein cofactors. We identify the orphan G-patch protein Cmg1 (YLR271W) as a novel cofactor of Prp43 and show that it stimulates the RNA binding and ATPase activity of the helicase.

MITRAC7 Acts as a COX1-Specific Chaperone and Reveals a Checkpoint during Cytochrome c Oxidase Assembly.

Cytochrome c oxidase, the terminal enzyme of the respiratory chain, is assembled from mitochondria- and nuclear-encoded subunits. The MITRAC complex represents the central assembly intermediate during this process as it receives imported subunits and regulates mitochondrial translation of COX1 mRNA. The molecular processes that promote and regulate the progression of assembly downstream of MITRAC are still unknown.

The INA complex facilitates assembly of the peripheral stalk of the mitochondrial F1Fo-ATP synthase.

Mitochondrial F1Fo-ATP synthase generates the bulk of cellular ATP. This molecular machine assembles from nuclear- and mitochondria-encoded subunits. Whereas chaperones for formation of the matrix-exposed hexameric F1-ATPase core domain have been identified, insight into how the nuclear-encoded F1-domain assembles with the membrane-embedded Fo-region is lacking.

Aim24 stabilizes respiratory chain supercomplexes and is required for efficient respiration.

The mitochondrial respiratory chain is essential for the conversion of energy derived from the oxidation of metabolites into the membrane potential, which drives the synthesis of ATP. The electron transporting complexes bc1 complex and the cytochrome c oxidase assemble into large supercomplexes, allowing efficient energy transduction. Currently, we have only limited information about what determines the structure of the supercomplex.

Uniform nomenclature for the mitochondrial contact site and cristae organizing system.

The mitochondrial inner membrane contains a large protein complex that functions in inner membrane organization and formation of membrane contact sites. The complex was variably named the mitochondrial contact site complex, mitochondrial inner membrane organizing system, mitochondrial organizing structure, or Mitofilin/Fcj1 complex. To facilitate future studies, we propose to unify the nomenclature and term the complex "mitochondrial contact site and cristae organizing system" and its subunits Mic10 to Mic60.

STED super-resolution microscopy reveals an array of MINOS clusters along human mitochondria.

The mitochondrial inner membrane organizing system (MINOS) is a conserved large hetero-oligomeric protein complex in the mitochondrial inner membrane, crucial for the maintenance of cristae morphology. MINOS has been suggested to represent the core of an extended protein network that controls mitochondrial function and structure, and has been linked to several human diseases. The spatial arrangement of MINOS within mitochondria is ill-defined, however.

The mitochondrial oxidase assembly protein1 (Oxa1) insertase forms a membrane pore in lipid bilayers.

The inner membrane of mitochondria is especially protein-rich. To direct proteins into the inner membrane, translocases mediate transport and membrane insertion of precursor proteins. Although the majority of mitochondrial proteins are imported from the cytoplasm, core subunits of respiratory chain complexes are inserted into the inner membrane from the matrix.

Rcf1 mediates cytochrome oxidase assembly and respirasome formation, revealing heterogeneity of the enzyme complex.

The terminal enzyme of the mitochondrial respiratory chain, cytochrome oxidase, transfers electrons to molecular oxygen, generating water. Within the inner mitochondrial membrane, cytochrome oxidase assembles into supercomplexes, together with other respiratory chain complexes, forming so-called respirasomes. Little is known about how these higher oligomeric structures are attained.

MINOS1 is a conserved component of mitofilin complexes and required for mitochondrial function and cristae organization.

The inner membrane of mitochondria is especially protein rich and displays a unique morphology characterized by large invaginations, the mitochondrial cristae, and the inner boundary membrane, which is in proximity to the outer membrane. Mitochondrial inner membrane proteins appear to be not evenly distributed in the inner membrane, but instead organize into functionally distinct subcompartments. It is unknown how the organization of the inner membrane is achieved.

Mdm38 is a 14-3-3-like receptor and associates with the protein synthesis machinery at the inner mitochondrial membrane.

Mitochondrial ribosomes synthesize core subunits of the inner membrane respiratory chain complexes. In mitochondria, translation is regulated by mRNA-specific activator proteins and occurs on membrane-associated ribosomes. Mdm38/Letm1 is a conserved membrane receptor for mitochondrial ribosomes and specifically involved in respiratory chain biogenesis.

Coa3 and Cox14 are essential for negative feedback regulation of COX1 translation in mitochondria.

Regulation of eukaryotic cytochrome oxidase assembly occurs at the level of Cox1 translation, its central mitochondria-encoded subunit. Translation of COX1 messenger RNA is coupled to complex assembly in a negative feedback loop: the translational activator Mss51 is thought to be sequestered to assembly intermediates, rendering it incompetent to promote translation. In this study, we identify Coa3 (cytochrome oxidase assembly factor 3; Yjl062w-A), a novel regulator of mitochondrial COX1 translation and cytochrome oxidase assembly.

Targeting of Pex8p to the peroxisomal importomer.

Pex8p of Saccharomyces cerevisiae is located at the inner surface of the peroxisomal membrane and is essential for the assembly of the importomer, a multi-protein complex of the peroxisomal protein import machinery. By means of the yeast two-hybrid system as well as in vitro binding studies, we demonstrate that Pex8p is capable to interact with the PTS2-receptor Pex7p and the docking complex component Pex13p with its C-terminal SH3-domain providing the binding site. Analysis of the importomer composition of pex-mutants revealed that both PTS-receptors as well as the auxiliary proteins Pex18p and Pex21p are neither required for Pex8p association with the importomer nor for its function as an organizer of the peroxisomal protein import machinery.

Ribosome-binding proteins Mdm38 and Mba1 display overlapping functions for regulation of mitochondrial translation.

Biogenesis of respiratory chain complexes depends on the expression of mitochondrial-encoded subunits. Their synthesis occurs on membrane-associated ribosomes and is probably coupled to their membrane insertion. Defects in expression of mitochondrial translation products are among the major causes of mitochondrial disorders.

Dynamin-related proteins Vps1p and Dnm1p control peroxisome abundance in Saccharomyces cerevisiae.

Saccharomyces cerevisiae contains three dynamin-related-proteins, Vps1p, Dnm1p and Mgm1p. Previous data from glucose-grown VPS1 and DNM1 null mutants suggested that Vps1p, but not Dnm1p, plays a role in regulating peroxisome abundance. Here we show that deletion of DNM1 also results in reduction of peroxisome numbers.