Sar1, a Novel Regulator of ER-Mitochondrial Contact Sites

Endoplasmic reticulum (ER)—mitochondrial contact sites play a pivotal role in exchange of lipids and ions between the two organelles. How size and function of these contact sites are regulated remains elusive. Here we report a previously unanticipated, but conserved role of the small GTPase Sar1 in the regulation of ER-mitochondrial contact site size. Activated Sar1 introduces membrane curvature through its N-terminal amphiphatic helix at the ER-mitochondria interphase and thereby reducing contact size. Conversely, the S. cerevisiae N3-Sar1 mutant, in which curvature induction is decreased, caused an increase in ER-mitochondrial contacts. As a consequence, ER tubules are no longer able to mark the prospective scission site on mitochondria, thereby impairing mitochondrial dynamics. Consistently, blocking mitochondrial fusion partially rescued, whereas deletion of the dynamin-like protein enhanced the phenotype in the sar1D32G mutant. We conclude that Sar1 regulates the size of ER-mitochondria contact sites through its effects on membrane curvature.

[1]  M. Labouesse.  [Caenorhabditis elegans]. , 2020, Medecine sciences : M/S.

[2]  M. Schuldiner,et al.  Lam6 Regulates the Extent of Contacts between Organelles , 2015, Cell reports.

[3]  P. De Camilli,et al.  Three-dimensional architecture of extended synaptotagmin-mediated endoplasmic reticulum–plasma membrane contact sites , 2015, Proceedings of the National Academy of Sciences.

[4]  F. Bard,et al.  The small GTPase Arf1 modulates mitochondrial morphology and function , 2014, The EMBO journal.

[5]  S. Stagg,et al.  Insights into the mechanisms of membrane curvature and vesicle scission by the small GTPase Sar1 in the early secretory pathway. , 2014, Journal of molecular biology.

[6]  Barry P. Young,et al.  A Conserved Endoplasmic Reticulum Membrane Protein Complex (EMC) Facilitates Phospholipid Transfer from the ER to Mitochondria , 2014, PLoS biology.

[7]  T. Katada,et al.  Concentration of Sec12 at ER exit sites via interaction with cTAGE5 is required for collagen export , 2014, The Journal of cell biology.

[8]  M. van der Laan,et al.  Cellular metabolism regulates contact sites between vacuoles and mitochondria. , 2014, Developmental cell.

[9]  M. Schuldiner,et al.  A dynamic interface between vacuoles and mitochondria in yeast. , 2014, Developmental cell.

[10]  T. Yorimitsu,et al.  Sec23 Homolog Nel1 Is a Novel GTPase-activating Protein for Sar1 but Does Not Function as a Subunit of the Coat Protein Complex II (COPII) Coat* , 2014, The Journal of Biological Chemistry.

[11]  M. Iijima,et al.  Effects of Fcj1-Mos1 and mitochondrial division on aggregation of mitochondrial DNA nucleoids and organelle morphology , 2013, Molecular biology of the cell.

[12]  P. Walter,et al.  ER-associated mitochondrial division links the distribution of mitochondria and mitochondrial DNA in yeast , 2013, eLife.

[13]  Barry P. Young,et al.  ER-shaping proteins facilitate lipid exchange between the ER and mitochondria in S. cerevisiae , 2012, Journal of Cell Science.

[14]  Christer S. Ejsing,et al.  Gem1 and ERMES Do Not Directly Affect Phosphatidylserine Transport from ER to Mitochondria or Mitochondrial Inheritance , 2012, Traffic.

[15]  S. Frank,et al.  A Tissue-Specific Approach to the Analysis of Metabolic Changes in Caenorhabditis elegans , 2011, PloS one.

[16]  Matthew West,et al.  ER Tubules Mark Sites of Mitochondrial Division , 2011, Science.

[17]  S. Emr,et al.  Osh Proteins Regulate Phosphoinositide Metabolism at ER-Plasma Membrane Contact Sites , 2011, Cell.

[18]  R. Parthasarathy,et al.  The vesicle trafficking protein Sar1 lowers lipid membrane rigidity. , 2010, Biophysical journal.

[19]  Simon C Watkins,et al.  Sar1 assembly regulates membrane constriction and ER export , 2010, The Journal of cell biology.

[20]  J. Nunnari,et al.  An ER-Mitochondria Tethering Complex Revealed by a Synthetic Biology Screen , 2009, Science.

[21]  J. Vandesompele,et al.  Selection and validation of a set of reliable reference genes for quantitative sod gene expression analysis in C. elegans , 2008, BMC Molecular Biology.

[22]  J. Shaw,et al.  Tetratricopeptide repeat proteins Tom70 and Tom71 mediate yeast mitochondrial morphogenesis , 2008, EMBO reports.

[23]  Simon C Watkins,et al.  Regulation of Sar1 NH2 terminus by GTP binding and hydrolysis promotes membrane deformation to control COPII vesicle fission , 2005, The Journal of cell biology.

[24]  Randy Schekman,et al.  Sar1p N-Terminal Helix Initiates Membrane Curvature and Completes the Fission of a COPII Vesicle , 2005, Cell.

[25]  I. Boldogh,et al.  A protein complex containing Mdm10p, Mdm12p, and Mmm1p links mitochondrial membranes and DNA to the cytoskeleton-based segregation machinery. , 2003, Molecular biology of the cell.

[26]  Y. Dong,et al.  Systematic functional analysis of the Caenorhabditis elegans genome using RNAi , 2003, Nature.

[27]  J. Nunnari,et al.  The WD repeat protein, Mdv1p, functions as a molecular adaptor by interacting with Dnm1p and Fis1p during mitochondrial fission , 2002, The Journal of cell biology.

[28]  H. Riezman,et al.  Ordering of Compartments in the Yeast Endocytic Pathway , 2002, Traffic.

[29]  M. Pfaffl,et al.  A new mathematical model for relative quantification in real-time RT-PCR. , 2001, Nucleic acids research.

[30]  Maithreyan Srinivasan,et al.  Mmm1p, a Mitochondrial Outer Membrane Protein, Is Connected to Mitochondrial DNA (Mtdna) Nucleoids and Required for Mtdna Stability , 2001, The Journal of cell biology.

[31]  N. Pfanner,et al.  Purification of Saccharomcyes cerevisiae mitochondria devoid of microsomal and cytosolic contaminations. , 2000, Analytical biochemistry.

[32]  W. Neupert,et al.  Mitochondria‐targeted green fluorescent proteins: convenient tools for the study of organelle biogenesis in Saccharomyces cerevisiae , 2000, Yeast.

[33]  W. Wickner,et al.  A Ypt/Rab effector complex containing the Sec1 homolog Vps33p is required for homotypic vacuole fusion. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[34]  P. Silver,et al.  Mutants Affecting the Structure of the Cortical Endoplasmic Reticulum in Saccharomyces cerevisiae , 2000, The Journal of cell biology.

[35]  R. Jensen,et al.  Division versus Fusion: Dnm1p and Fzo1p Antagonistically Regulate Mitochondrial Shape , 1999, The Journal of cell biology.

[36]  A. M. van der Bliek,et al.  C. elegans dynamin-related protein DRP-1 controls severing of the mitochondrial outer membrane. , 1999, Molecular cell.

[37]  K. Siegers,et al.  Epitope tagging of yeast genes using a PCR‐based strategy: more tags and improved practical routines , 1999, Yeast.

[38]  O. Rossanese,et al.  Golgi Structure Correlates with Transitional Endoplasmic Reticulum Organization in Pichia pastoris and Saccharomyces cerevisiae , 1999, The Journal of cell biology.

[39]  J. Thatcher,et al.  Mitochondrial Fusion in Yeast Requires the Transmembrane GTPase Fzo1p , 1998, The Journal of cell biology.

[40]  W. Neupert,et al.  Fzo1p Is a Mitochondrial Outer Membrane Protein Essential for the Biogenesis of Functional Mitochondria in Saccharomyces cerevisiae* , 1998, The Journal of Biological Chemistry.

[41]  A. Nakano,et al.  Identification of a gene required for membrane protein retention in the early secretory pathway. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[42]  V. Ambros,et al.  Efficient gene transfer in C.elegans: extrachromosomal maintenance and integration of transforming sequences. , 1991, The EMBO journal.

[43]  R. Schiestl,et al.  High efficiency transformation of intact yeast cells using single stranded nucleic acids as a carrier , 1989, Current Genetics.

[44]  N. Munakata.  [Genetics of Caenorhabditis elegans]. , 1989, Tanpakushitsu kakusan koso. Protein, nucleic acid, enzyme.

[45]  N. Pfanner,et al.  Isolation of yeast mitochondria. , 2006, Methods in molecular biology.

[46]  A. Nakano,et al.  Identification of SEC12, SED4, truncated SEC16, and EKS1/HRD3 as multicopy suppressors of ts mutants of Sar1 GTPase. , 1999, Journal of biochemistry.

[47]  A. Labrousse,et al.  elegans Dynamin-Related Protein DRP-1 Controls Severing of the Mitochondrial Outer , 1999 .

[48]  F. Sherman.  Getting started with yeast. , 1991, Methods in enzymology.