An ER-Mitochondria Tethering Complex Revealed by a Synthetic Biology Screen

Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, CA 94158, USA.
Science (Impact Factor: 33.61). 07/2009; 325(5939):477-81. DOI: 10.1126/science.1175088
Source: PubMed


Communication between organelles is an important feature of all eukaryotic cells. To uncover components involved in mitochondria/endoplasmic reticulum (ER) junctions, we screened for mutants that could be complemented by a synthetic protein designed to artificially tether the two organelles. We identified the Mmm1/Mdm10/Mdm12/Mdm34 complex as a molecular tether between ER and mitochondria. The tethering complex was composed of proteins resident of both ER and mitochondria. With the use of genome-wide mapping of genetic interactions, we showed that the components of the tethering complex were functionally connected to phospholipid biosynthesis and calcium-signaling genes. In mutant cells, phospholipid biosynthesis was impaired. The tethering complex localized to discrete foci, suggesting that discrete sites of close apposition between ER and mitochondria facilitate interorganelle calcium and phospholipid exchange.

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    • "According to one study, deletion of ERMES components alters PS conversion to PC, demonstrating that the ERMES complex is required for optimal lipid exchange between cellular compartments. These defects can be partially rescued by the expression of an artificial ER–mitochondrial tether, suggesting that close membrane proximity alone can facilitate transfer [22] [23]. Nevertheless, another study by Nguyen et al. shows that the deletion of ERMES proteins in yeast neither directly affects PS to PE conversion nor alters mitochondrial inheritance, because both these effects are secondary to morphological changes in mitochondria [25]. "
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    ABSTRACT: Eukaryotic cells contain a variety of subcellular organelles, each of which performs unique tasks. Thus follows that in order to coordinate these different intracellular functions, a highly dynamic system of communication must exist between the various compartments. Direct endoplasmic reticulum (ER)-mitochondria communication is facilitated by the physical interaction of their membranes in dedicated structural domains known as mitochondria-associated membranes (MAM), which facilitate calcium (Ca(2+)) and lipid transfer between organelles and also act as platforms for signaling. Numerous studies have demonstrated the importance of MAM in ensuring correct function of both organelles, and recently MAM have been implicated in the genesis of various human diseases. Here, we review the salient structural features of interorganellar communication via MAM and discuss the most common experimental techniques employed to assess functionality of these domains. Finally, we will highlight the contribution of MAM to variety cellular functions and consider the potential role of MAM in the genesis of metabolic diseases. In doing so, the importance for cell functions of maintaining appropriate communication between ER and mitochondria will be emphasized. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta 07/2015; 1852(10 Pt A). DOI:10.1016/j.bbadis.2015.07.011 · 4.66 Impact Factor
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    • "Moreover, deletion of any of the ERMES subunits did not alter the punctate pattern of Lam6-GFP, suggesting that the ERMES complex is not important for its recruitment (Figure S1B). In addition, unlike ERMES mutants, which are characterized by having abnormal mitochondria shape, impaired growth rate, and an inability to grow on a non-fermentable carbon source (Kornmann et al., 2009), loss of LAM6 did not affect growth on either a fermentable or non-fermentable carbon source (Figure S1C), mitochondrial morphology (Figure S1D), or the levels of a variety of mitochondrial proteins (Figure S1A). Interestingly, overexpressing Lam6 had no effect on growth or mitochondrial morphology, even on the background of Dmdm34 (Figures S1C and S1D). "
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    ABSTRACT: Communication between organelles is crucial for eukaryotic cells to function as one coherent unit. An important means of communication is through membrane contact sites, where two organelles come into close proximity allowing the transport of lipids and small solutes between them. Contact sites are dynamic in size and can change in response to environmental or cellular stimuli; however, how this is regulated has been unclear. Here, we show that Saccharomyces cerevisiae Lam6 resides in several central contact sites: ERMES (ER/mitochondria encounter structure), vCLAMP (vacuole and mitochondria patch), and NVJ (nuclear vacuolar junction). We show that Lam6 is sufficient for expansion of contact sites under physiological conditions and necessary for coordination of contact site size. Given that Lam6 is part of a large protein family and is conserved in vertebrates, our work opens avenues for investigating the underlying principles of organelle communication. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Cell Reports 06/2015; 12(1). DOI:10.1016/j.celrep.2015.06.022 · 8.36 Impact Factor
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    • "How then could a resident protein of the ER affect mtDNA segregation? Interactions between the ER and mitochondria play a key role in many aspects of mitochondrial homeostasis, such as morphology of the mitochondrial reticulum (division and tethering of the organelle), calcium handling, lipid transfer, and transmission of the mitochondrial genome among others (de Brito and Scorrano 2008; Kornmann et al. 2009; Friedman et al. 2011; Hoppins et al. 2011; Connerth et al. 2012; Rowland and Voeltz 2012; Korobova et al. 2013; Hajnoczky et al. 2014). "
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    ABSTRACT: Mammalian mitochondrial DNA (mtDNA) is a high-copy maternally inherited genome essential for aerobic energy metabolism. Mutations in mtDNA can lead to heteroplasmy, the co-occurrence of two different mtDNA variants in the same cell, which can segregate in a tissue-specific manner affecting the onset and severity of mitochondrial dysfunction. To investigate mechanisms regulating mtDNA segregation we use a heteroplasmic mouse model with two polymorphic neutral mtDNA haplotypes (NZB and BALB) that displays tissue-specific and age-dependent selection for mtDNA haplotypes. In the hematopoietic compartment there is selection for the BALB mtDNA haplotype, a phenotype that can be modified by allelic variants of Gimap3. Gimap3 is a tail-anchored member of the GTPase of the immunity-associated protein (Gimap) family of protein scaffolds important for leukocyte development and survival. Here we show how the expression of two murine Gimap3 alleles from Mus musculus domesticus and M. m. castaneus differentially affect mtDNA segregation. The castaneus allele has incorporated a uORF (upstream open reading frame) in-frame with the Gimap3 mRNA that impairs translation and imparts a negative effect on the steady-state protein abundance. We found that quantitative changes in the expression of Gimap3 and the paralogue Gimap5, which encodes a lysosomal protein, affect mtDNA segregation in the mouse hematopoietic tissues. We also show that Gimap3 localizes to the endoplasmic reticulum and not mitochondria as previously reported. Collectively these data show that the abundance of protein scaffolds on the endoplasmic reticulum and lysosomes are important to the segregation of the mitochondrial genome in the mouse hematopoietic compartment. Copyright © 2015, The Genetics Society of America.
    Genetics 03/2015; 200(1). DOI:10.1534/genetics.115.175596 · 5.96 Impact Factor
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