scholarly journals Cytosolic Hsp70 and Hsp40 chaperones enable the biogenesis of mitochondrial β-barrel proteins

2018 ◽  
Vol 217 (9) ◽  
pp. 3091-3108 ◽  
Author(s):  
Tobias Jores ◽  
Jannis Lawatscheck ◽  
Viktor Beke ◽  
Mirita Franz-Wachtel ◽  
Kaori Yunoki ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Mammalian Cells ◽  
Mitochondrial Outer Membrane ◽  
Detailed Understanding ◽  
Cytosolic Ribosomes

Mitochondrial β-barrel proteins are encoded in the nucleus, translated by cytosolic ribosomes, and then imported into the organelle. Recently, a detailed understanding of the intramitochondrial import pathway of β-barrel proteins was obtained. In contrast, it is still completely unclear how newly synthesized β-barrel proteins reach the mitochondrial surface in an import-competent conformation. In this study, we show that cytosolic Hsp70 chaperones and their Hsp40 cochaperones Ydj1 and Sis1 interact with newly synthesized β-barrel proteins. These interactions are highly relevant for proper biogenesis, as inhibiting the activity of the cytosolic Hsp70, preventing its docking to the mitochondrial receptor Tom70, or depleting both Ydj1 and Sis1 resulted in a significant reduction in the import of such substrates into mitochondria. Further experiments demonstrate that the interactions between β-barrel proteins and Hsp70 chaperones and their importance are conserved also in mammalian cells. Collectively, this study outlines a novel mechanism in the early events of the biogenesis of mitochondrial outer membrane β-barrel proteins.

scholarly journals OM14 is a mitochondrial receptor for cytosolic ribosomes that supports co-translational import into mitochondria

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Chen Lesnik ◽  
Yifat Cohen ◽  
Avigail Atir-Lande ◽  
Maya Schuldiner ◽  
Yoav Arava
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Membrane Protein ◽  
Outer Membrane ◽  
Outer Membrane Protein ◽  
Strong Support ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Import ◽  
Translational Mode ◽  
Nascent Chain ◽  
Cytosolic Ribosomes

Abstract It is well established that import of proteins into mitochondria can occur after their complete synthesis by cytosolic ribosomes. Recently, an additional model was revived, proposing that some proteins are imported co-translationally. This model entails association of ribosomes with the mitochondrial outer membrane, shown to be mediated through the ribosome-associated chaperone nascent chain-associated complex (NAC). However, the mitochondrial receptor of this complex is unknown. Here, we identify the Saccharomyces cerevisiae outer membrane protein OM14 as a receptor for NAC. OM14Δ mitochondria have significantly lower amounts of associated NAC and ribosomes, and ribosomes from NAC[Δ] cells have reduced levels of associated OM14. Importantly, mitochondrial import assays reveal a significant decrease in import efficiency into OM14Δ mitochondria, and OM14-dependent import necessitates NAC. Our results identify OM14 as the first mitochondrial receptor for ribosome-associated NAC and reveal its importance for import. These results provide a strong support for an additional, co-translational mode of import into mitochondria.

Mitochondrial outer-membrane protein FUNDC1 mediates hypoxia-induced mitophagy in mammalian cells

2012 ◽  
Vol 14 (2) ◽  
pp. 177-185 ◽  
Author(s):  
Lei Liu ◽  
Du Feng ◽  
Guo Chen ◽  
Ming Chen ◽  
Qiaoxia Zheng ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Outer Membrane ◽  
Outer Membrane Protein ◽  
Mammalian Cells ◽  
Mitochondrial Outer Membrane

scholarly journals The Mitochondrial Outer Membrane Protein Tom70-Mediator in Protein Traffic, Membrane Contact Sites and Innate Immunity

2020 ◽  
Vol 21 (19) ◽  
pp. 7262
Author(s):  
Sebastian Kreimendahl ◽  
Joachim Rassow
Keyword(s):  
Innate Immunity ◽  
Outer Membrane ◽  
Mammalian Cells ◽  
Tertiary Structure ◽  
Viral Infections ◽  
Adaptor Protein ◽  
Type I Interferons ◽  
Mitochondrial Outer Membrane ◽  
Type I ◽  
Membrane Contact Sites

Tom70 is a versatile adaptor protein of 70 kDa anchored in the outer membrane of mitochondria in metazoa, fungi and amoeba. The tertiary structure was resolved for the Tom70 of yeast, showing 26 α-helices, most of them participating in the formation of 11 tetratricopeptide repeat (TPR) motifs. Tom70 serves as a docking site for cytosolic chaperone proteins and co-chaperones and is thereby involved in the uptake of newly synthesized chaperone-bound proteins in mitochondrial biogenesis. In yeast, Tom70 additionally mediates ER-mitochondria contacts via binding to sterol transporter Lam6/Ltc1. In mammalian cells, TOM70 promotes endoplasmic reticulum (ER) to mitochondria Ca2+ transfer by association with the inositol-1,4,5-triphosphate receptor type 3 (IP3R3). TOM70 is specifically targeted by the Bcl-2-related protein MCL-1 that acts as an anti-apoptotic protein in macrophages infected by intracellular pathogens, but also in many cancer cells. By participating in the recruitment of PINK1 and the E3 ubiquitin ligase Parkin, TOM70 can be implicated in the development of Parkinson’s disease. TOM70 acts as receptor of the mitochondrial antiviral-signaling protein (MAVS) and thereby participates in the corresponding system of innate immunity against viral infections. The protein encoded by Orf9b in the genome of SARS-CoV-2 binds to TOM70, probably compromising the synthesis of type I interferons.

Biogenesis pathways of α-helical mitochondrial outer membrane proteins

2020 ◽  
Vol 401 (6-7) ◽  
pp. 677-686 ◽  
Author(s):  
Layla Drwesh ◽  
Doron Rapaport
Keyword(s):  
Membrane Proteins ◽  
Outer Membrane ◽  
Protein Import ◽  
Nuclear Dna ◽  
Current Knowledge ◽  
Outer Membrane Proteins ◽  
Mitochondrial Outer Membrane ◽  
Cytosolic Ribosomes

AbstractMitochondria harbor in their outer membrane (OM) proteins of different topologies. These proteins are encoded by the nuclear DNA, translated on cytosolic ribosomes and inserted into their target organelle by sophisticated protein import machineries. Recently, considerable insights have been accumulated on the insertion pathways of proteins into the mitochondrial OM. In contrast, little is known regarding the early cytosolic stages of their biogenesis. It is generally presumed that chaperones associate with these proteins following their synthesis in the cytosol, thereby keeping them in an import-competent conformation and preventing their aggregation and/or mis-folding and degradation. In this review, we outline the current knowledge about the biogenesis of different mitochondrial OM proteins with various topologies, and highlight the recent findings regarding their import pathways starting from early cytosolic events until their recognition on the mitochondrial surface that lead to their final insertion into the mitochondrial OM.

scholarly journals Regulation of Mitochondrial Morphology by USP30, a Deubiquitinating Enzyme Present in the Mitochondrial Outer Membrane

2008 ◽  
Vol 19 (5) ◽  
pp. 1903-1911 ◽  
Author(s):  
Nobuhiro Nakamura ◽  
Shigehisa Hirose
Keyword(s):  
Outer Membrane ◽  
Mammalian Cells ◽  
Mitochondrial Dynamics ◽  
Ectopic Expression ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Deubiquitinating Enzyme ◽  
Human Ubiquitin ◽  
Specific Protease ◽  
Insight Into

Recent studies have suggested that ubiquitination of mitochondrial proteins participates in regulating mitochondrial dynamics in mammalian cells, but it is unclear whether deubiquitination is involved in this process. Here, we identify human ubiquitin-specific protease 30 (USP30) as a deubiquitinating enzyme that is embedded in the mitochondrial outer membrane. Depletion of USP30 expression by RNA interference induced elongated and interconnected mitochondria, depending on the activities of the mitochondrial fusion factors mitofusins, without changing the expression levels of the key regulators for mitochondrial dynamics. Mitochondria were rescued from this abnormal phenotype by ectopic expression of USP30 in a manner dependent on its enzymatic activity. Our findings reveal that USP30 participates in the maintenance of mitochondrial morphology, a finding that provides new insight into the cellular function of deubiquitination.

scholarly journals A novel, high conductance channel of mitochondria linked to apoptosis in mammalian cells and Bax expression in yeast

2001 ◽  
Vol 155 (5) ◽  
pp. 725-732 ◽  
Author(s):  
Evgeny V. Pavlov ◽  
Muriel Priault ◽  
Dawn Pietkiewicz ◽  
Emily H.-Y. Cheng ◽  
Bruno Antonsson ◽  
...  
Keyword(s):  
Cytochrome C ◽  
Outer Membrane ◽  
Mammalian Cells ◽  
Pore Diameter ◽  
Mitochondrial Outer Membrane ◽  
Channel Activity ◽  
Patch Clamping ◽  
Membrane Pore ◽  
Outer Membranes ◽  
High Conductance

During apoptosis, proapoptotic factors are released from mitochondria by as yet undefined mechanisms. Patch-clamping of mitochondria and proteoliposomes formed from mitochondrial outer membranes of mammalian (FL5.12) cells has uncovered a novel ion channel whose activity correlates with onset of apoptosis. The pore diameter inferred from the largest conductance state of this channel is ∼4 nm, sufficient to allow diffusion of cytochrome c and even larger proteins. The activity of the channel is affected by Bcl-2 family proteins in a manner consistent with their pro- or antiapoptotic properties. Thus, the channel activity correlates with presence of proapoptotic Bax in the mitochondrial outer membrane and is absent in mitochondria from cells overexpressing antiapoptotic Bcl-2. Also, a similar channel activity is found in mitochondrial outer membranes of yeast expressing human Bax. These findings implicate this channel, named mitochondrial apoptosis–induced channel, as a candidate for the outer-membrane pore through which cytochrome c and possibly other factors exit mitochondria during apoptosis.

Cryo-Electron Microscopy and Correlation Averaging of Frozen-Hydrated, Polymorphic 2D Crystals of the Mitochondrial Outer Membrane Channel

1990 ◽  
Vol 48 (1) ◽  
pp. 100-101
Author(s):  
Xiao-Wei Guo
Keyword(s):  
Outer Membrane ◽  
Hexagonal Lattice ◽  
Mitochondrial Outer Membrane ◽  
Rectangular Lattice ◽  
Electron Microscopic ◽  
Cryo Electron Microscopy ◽  
Voltage Dependent ◽  
Outer Membrane Channel ◽  
2D Crystals ◽  
Vdac Channel

Voltage-dependent, anion-selective channels (VDAC) are formed in the mitochondrial outer membrane (mitOM) by a 30-kDa polypeptide. These channels form ordered 2D arrays when mitOMs from Neurospora crassa are treated with soluble phospholipase A2. We obtain low-dose electron microscopic images of unstained specimens of VDAC crystals preserved in vitreous ice, using a Philips EM420 equipped with a Gatan cryo-transfer stage. We then use correlation analysis to compute average projections of the channel crystals. The procedure involves Fourier-filtration of a region within a crystal field to obtain a preliminary average that is subsequently cross-correlated with the entire crystal. Subregions are windowed from the crystal image at coordinates of peaks in the cross-correlation function (CCF, see Figures 1 and 2) and summed to form averages (Figure 3).The VDAC channel forms several different types of crystalline arrays in mitOMs. The polymorph first observed during phospholipase treatment is a parallelogram array (a=13 run, b=11.5 run, θ==109°) containing 6 water-filled pores per unit cell. Figure 1 shows the CCF of a sub-field of such an “oblique” array used to compute the correlation average of Figure 3A. With increased phospholipase treatment, other polymorphs are observed, often co-existing within the same crystal. For example, two distinct (but closely related) types of lattices occur in the field corresponding to the CCF of Figure 2: a “contracted” version of the parallelogram lattice (a=13 run, b=10 run, θ=99°), and a near-rectangular lattice (a=8.5 run, b=5 nm). The pattern of maxima in this CCF suggests that a third, near-hexagonal lattice (a=4.5 nm) may also be present. The correlation averages of Figures 3B-D were computed from polycrystalline fields, using peak coordinates in regions of CCFs corresponding to each of the three lattice types.

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