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The Journal of Cell Biology Feb 2009Mitochondrial membrane biogenesis requires the import and synthesis of proteins as well as phospholipids. How the mitochondrion regulates phospholipid levels and... (Review)
Review
Mitochondrial membrane biogenesis requires the import and synthesis of proteins as well as phospholipids. How the mitochondrion regulates phospholipid levels and maintains a tight protein-to-phospholipid ratio is not well understood. Two recent papers (Kutik, S., M. Rissler, X.L. Guan, B. Guiard, G. Shui, N. Gebert, P.N. Heacock, P. Rehling, W. Dowhan, M.R. Wenk, et al. 2008. J. Cell Biol. 183:1213-1221; Osman, C., M. Haag, C. Potting, J. Rodenfels, P.V. Dip, F.T. Wieland, B. Brügger, B. Westermann, and T. Langer. 2009. J. Cell Biol. 184:583-596) identify novel regulators of mitochondrial phospholipid biosynthesis. The biochemical approach of Kutik et al. (2008) uncovered an unexpected role of the mitochondrial translocator assembly and maintenance protein, Tam41, in the biosynthesis of cardiolipin (CL), the signature phospholipid of mitochondria. The genetic analyses of Osman et al. (2009) led to the discovery of a new class of mitochondrial proteins that coordinately regulate CL and phosphatidylethanolamine, another key mitochondrial phospholipid. These elegant studies highlight overlapping functions and interdependent roles of mitochondrial phospholipid biosynthesis and protein import and assembly.
Topics: Animals; Biosynthetic Pathways; Humans; Mitochondrial Membranes; Mitochondrial Proteins; Phospholipids
PubMed: 19237595
DOI: 10.1083/jcb.200901127 -
FEBS Letters Jun 2023Mitochondria are organelles indispensable for the correct functioning of eukaryotic cells. Their significance for cellular homeostasis is manifested by the existence of... (Review)
Review
Mitochondria are organelles indispensable for the correct functioning of eukaryotic cells. Their significance for cellular homeostasis is manifested by the existence of complex quality control pathways that monitor organellar fitness. Mitochondrial biogenesis relies on the efficient import of mitochondrial precursor proteins, a large majority of which are encoded by nuclear DNA and synthesized in the cytosol. This creates a demand for highly specialized import routes that comprise cytosolic factors and organellar translocases. The passage of newly encoded mitochondrial precursor proteins through the cytosol to the translocase of the outer mitochondrial membrane (TOM) is under tight surveillance. As a result of mitochondrial import defects, mitochondrial precursor proteins accumulate in the cytosol or clog the TOM complex, which in turn stimulates cellular stress responses to minimize the consequences of these challenges. These responses are critical for maintaining protein homeostasis under conditions of mitochondrial stress. The present review summarizes recent advances in the field of mitochondrial protein import quality control and discusses the role of this quality control within the network of cellular mechanisms that maintain the cellular homeostasis of proteins.
Topics: Proteostasis; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins; Carrier Proteins; Protein Transport; Homeostasis
PubMed: 37276075
DOI: 10.1002/1873-3468.14677 -
Seminars in Cell & Developmental Biology Mar 2024Membrane structural integrity is essential for optimal mitochondrial function. These organelles produce the energy needed for all vital processes, provided their outer... (Review)
Review
Membrane structural integrity is essential for optimal mitochondrial function. These organelles produce the energy needed for all vital processes, provided their outer and inner membranes are intact. This prevents the release of mitochondrial apoptogenic factors into the cytosol and ensures intact mitochondrial membrane potential (ΔΨ) to sustain ATP production. Cell death by apoptosis is generally triggered by outer mitochondrial membrane permeabilization (MOMP), tightly coupled with loss of ΔΨ . As these two processes are essential for both mitochondrial function and cell death, researchers have devised various techniques to assess them. Here, we discuss current methods and biosensors available for detecting MOMP and measuring ΔΨ , focusing on their advantages and limitations and discuss what new imaging tools are needed to improve our knowledge of mitochondrial function.
Topics: Mitochondrial Membranes; Membrane Potentials; Mitochondria; Apoptosis; Biosensing Techniques
PubMed: 37438211
DOI: 10.1016/j.semcdb.2023.07.003 -
Molecular Cell Apr 2015In this and a recent issue of Molecular Cell, Liu et al. (2015) and Ichim et al. (2015) report that low levels of caspase activity triggered by limited mitochondrial...
In this and a recent issue of Molecular Cell, Liu et al. (2015) and Ichim et al. (2015) report that low levels of caspase activity triggered by limited mitochondrial outer membrane permeabilization (MOMP) promote genomic instability that drives tumorigenesis, providing a novel and unexpected link between these effectors of apoptosis and cancer initiation.
Topics: Animals; Apoptosis; DNA Damage; Genomic Instability; Humans; Mitochondrial Membranes
PubMed: 25884366
DOI: 10.1016/j.molcel.2015.03.035 -
Cell Reports Sep 2022Mitochondria are dynamic organelles essential for cell survival whose structural and functional integrity rely on selective and regulated transport of lipids from/to the...
Mitochondria are dynamic organelles essential for cell survival whose structural and functional integrity rely on selective and regulated transport of lipids from/to the endoplasmic reticulum (ER) and across the mitochondrial intermembrane space. As they are not connected by vesicular transport, the exchange of lipids between ER and mitochondria occurs at membrane contact sites. However, the mechanisms and proteins involved in these processes are only beginning to emerge. Here, we show that the main physiological localization of the lipid transfer proteins ORP5 and ORP8 is at mitochondria-associated ER membrane (MAM) subdomains, physically linked to the mitochondrial intermembrane space bridging (MIB)/mitochondrial contact sites and cristae junction organizing system (MICOS) complexes that bridge the two mitochondrial membranes. We also show that ORP5/ORP8 mediate non-vesicular transport of phosphatidylserine (PS) lipids from the ER to mitochondria by cooperating with the MIB/MICOS complexes. Overall our study reveals a physical and functional link between ER-mitochondria contacts involved in lipid transfer and intra-mitochondrial membrane contacts maintained by the MIB/MICOS complexes.
Topics: Endoplasmic Reticulum; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins; Phosphatidylserines
PubMed: 36130504
DOI: 10.1016/j.celrep.2022.111364 -
Biochimica Et Biophysica Acta.... Jan 2021The inner membrane of mitochondria is known for its low lipid-to-protein ratio. Calculations based on the size and the concentration of the principal membrane... (Review)
Review
The inner membrane of mitochondria is known for its low lipid-to-protein ratio. Calculations based on the size and the concentration of the principal membrane components, suggest about half of the hydrophobic volume of the membrane is occupied by proteins. Such high degree of crowding is expected to strain the hydrophobic coupling between proteins and lipids unless stabilizing mechanisms are in place. Both protein supercomplexes and cardiolipin are likely to be critical for the integrity of the inner mitochondrial membrane because they reduce the energy penalty of crowding.
Topics: Animals; Humans; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins
PubMed: 32916174
DOI: 10.1016/j.bbabio.2020.148305 -
Biochimica Et Biophysica Acta.... Sep 2017Mitochondria are multifunctional metabolic factories and integrative signaling organelles of eukaryotic cells. The structural basis for their numerous functions is a... (Review)
Review
Mitochondria are multifunctional metabolic factories and integrative signaling organelles of eukaryotic cells. The structural basis for their numerous functions is a complex and dynamic double-membrane architecture. The outer membrane connects mitochondria to the cytosol and other organelles. The inner membrane is composed of a boundary region and highly folded cristae membranes. The evolutionarily conserved mitochondrial contact site and cristae organizing system (MICOS) connects the two inner membrane domains via formation and stabilization of crista junction structures. Moreover, MICOS establishes contact sites between inner and outer mitochondrial membranes by interacting with outer membrane protein complexes. MICOS deficiency leads to a grossly altered inner membrane architecture resulting in far-reaching functional perturbations in mitochondria. Consequently, mutations affecting the function of MICOS are responsible for a diverse spectrum of human diseases. In this article, we summarize recent insights and concepts on the role of MICOS in the organization of mitochondrial membranes. This article is part of a Special Issue entitled: Membrane Contact Sites edited by Christian Ungermann and Benoit Kornmann.
Topics: Animals; Humans; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Membranes; Signal Transduction
PubMed: 28526561
DOI: 10.1016/j.bbamcr.2017.05.004 -
Biochemistry Sep 2017The inner mitochondrial membrane (IM) is among the most protein-rich cellular compartments. The metastable IM subproteome where the concentration of proteins is... (Review)
Review
The inner mitochondrial membrane (IM) is among the most protein-rich cellular compartments. The metastable IM subproteome where the concentration of proteins is approaching oversaturation creates a challenging protein folding environment with a high probability of protein malfunction or aggregation. Failure to maintain protein homeostasis in such a setting can impair the functional integrity of the mitochondria and drive clinical manifestations. The IM is equipped with a series of highly conserved, proteolytic complexes dedicated to the maintenance of normal protein homeostasis within this mitochondrial subcompartment. Particularly important is a group of membrane-anchored metallopeptidases commonly known as m-AAA and i-AAA proteases, and the ATP-independent Oma1 protease. Herein, we will summarize the current biochemical knowledge of these proteolytic machines and discuss recent advances in our understanding of mechanistic aspects of their functioning.
Topics: Animals; Gene Expression Regulation, Enzymologic; Homeostasis; Metalloproteases; Mitochondrial Membranes; Protein Conformation
PubMed: 28806058
DOI: 10.1021/acs.biochem.7b00663 -
FASEB Journal : Official Publication of... Jan 2021Mitochondrial membrane potential (ΔΨm) is a global indicator of mitochondrial function. Previous reports on heterogeneity of ΔΨm were qualitative or...
Mitochondrial membrane potential (ΔΨm) is a global indicator of mitochondrial function. Previous reports on heterogeneity of ΔΨm were qualitative or semiquantitative. Here, we quantified intercellular differences in ΔΨm in unsynchronized human cancer cells, cells synchronized in G1, S, and G2, and human fibroblasts. We assessed ΔΨm using a two-pronged microscopy approach to measure relative fluorescence of tetramethylrhodamine methyl ester (TMRM) and absolute values of ΔΨm. We showed that ΔΨm is more heterogeneous in cancer cells compared to fibroblasts, and it is maintained throughout the cell cycle. The effect of chemical inhibition of the respiratory chain and ATP synthesis differed between basal, low and high ΔΨm cells. Overall, our results showed that intercellular heterogeneity of ΔΨm is mainly modulated by intramitochondrial factors, it is independent of the ΔΨm indicator and it is not correlated with intercellular heterogeneity of plasma membrane potential or the phases of the cell cycle.
Topics: Cell Cycle; Hep G2 Cells; Humans; Membrane Potential, Mitochondrial; Mitochondria; Mitochondrial Membranes; Neoplasms
PubMed: 33196122
DOI: 10.1096/fj.202001693R -
Methods in Molecular Biology (Clifton,... 2017The isolation and characterization of mitochondrial membrane proteins is technically challenging because they natively reside within the specialized environment of the...
The isolation and characterization of mitochondrial membrane proteins is technically challenging because they natively reside within the specialized environment of the lipid bilayer, an environment that must be recapitulated to some degree during reconstitution to ensure proper folding, stability, and function. Here we describe protocols for the assembly of a membrane protein into lipid bilayer nanodiscs in a series of cell-free reactions. Cell-free expression of membrane proteins circumvents problems attendant with in vivo expression such as cytotoxicity, low expression levels, and the formation of inclusion bodies. Nanodiscs are artificial membrane systems comprised of discoidal lipid bilayer particles bound by annuli of amphipathic scaffold protein that shield lipid acyl chains from water. They are therefore excellent platforms for membrane protein reconstitution and downstream solution-based biochemical and biophysical analysis. This chapter details the procedures for the reconstitution of a mitochondrial membrane protein into nanodiscs using two different types of approaches: cotranslational and posttranslational assembly. These strategies are broadly applicable for different mitochondrial membrane proteins. They are also applicable for the use of nanodiscs with distinct lipid compositions that are biomimetic for different mitochondrial membranes and that recapitulate lipid profiles associated with pathological disorders in lipid metabolism.
Topics: Cell-Free System; In Vitro Techniques; Lipid Bilayers; Membrane Proteins; Mitochondrial Membranes; Nanostructures; Protein Binding; Protein Biosynthesis; Triticum; Workflow
PubMed: 28276018
DOI: 10.1007/978-1-4939-6824-4_10