scholarly journals Bridging the gap: Membrane contact sites in signaling, metabolism, and organelle dynamics

2014 ◽  
Vol 205 (6) ◽  
pp. 759-769 ◽  
Author(s):  
William A. Prinz
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Intracellular Signaling ◽  
Close Apposition ◽  
Organelle Inheritance ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact

Regions of close apposition between two organelles, often referred to as membrane contact sites (MCSs), mostly form between the endoplasmic reticulum and a second organelle, although contacts between mitochondria and other organelles have also begun to be characterized. Although these contact sites have been noted since cells first began to be visualized with electron microscopy, the functions of most of these domains long remained unclear. The last few years have witnessed a dramatic increase in our understanding of MCSs, revealing the critical roles they play in intracellular signaling, metabolism, the trafficking of metabolites, and organelle inheritance, division, and transport.

Mitochondria–organelle contact sites: the plot thickens

2017 ◽  
Vol 45 (2) ◽  
pp. 477-488 ◽  
Author(s):  
Yael Elbaz-Alon
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Cellular Metabolism ◽  
Close Apposition ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Cellular Organelles

Membrane contact sites (MCSs) are areas of close apposition between the membranes of two different organelles that enable non-vesicular transfer of ions and lipids. Recent studies reveal that mitochondria maintain contact sites with organelles other than the endoplasmic reticulum such as the vacuole, plasma membrane and peroxisomes. This review focuses on novel findings achieved mainly in yeast regarding tethers, function and regulation of mitochondria–organelle contact sites. The emerging network of MCSs linking virtually all cellular organelles is highly dynamic and integrated with cellular metabolism.

scholarly journals The Interactome of the VAP Family of Proteins: An Overview

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1780
Author(s):  
Christina James ◽  
Ralph H. Kehlenbach
Keyword(s):  
Endoplasmic Reticulum ◽  
Calcium Homeostasis ◽  
In Silico ◽  
Lipid Transport ◽  
Biological Processes ◽  
Close Apposition ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Associated Proteins ◽  
Membrane Contact

Membrane contact sites (MCS) are sites of close apposition of two organelles that help in lipid transport and synthesis, calcium homeostasis and several other biological processes. The VAMP-associated proteins (VAPs) VAPA, VAPB, MOSPD2 and the recently described MOSPD1 and MOSPD3 are tether proteins of MCSs that are mainly found at the endoplasmic reticulum (ER). VAPs interact with various proteins with a motif called FFAT (two phenylalanines in an acidic tract), recruiting the associated organelle to the ER. In addition to the conventional FFAT motif, the recently described FFNT (two phenylalanines in a neutral tract) and phospho-FFAT motifs contribute to the interaction with VAPs. In this review, we summarize and compare the recent interactome studies described for VAPs, including in silico and proximity labeling methods. Collectively, the interaction repertoire of VAPs is very diverse and highlights the complexity of interactions mediated by the different FFAT motifs to the VAPs.

scholarly journals Synaptotagmins at the endoplasmic reticulum–plasma membrane contact sites maintain diacylglycerol homeostasis during abiotic stress

2021 ◽  
Author(s):  
Noemi Ruiz-Lopez ◽  
Jessica Pérez-Sancho ◽  
Alicia Esteban del Valle ◽  
Richard P Haslam ◽  
Steffen Vanneste ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Abiotic Stress ◽  
Fluorescent Protein ◽  
Mechanical Damage ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Green Fluorescent

Abstract Endoplasmic reticulum-plasma membrane contact sites (ER-PM CS) play fundamental roles in all eukaryotic cells. Arabidopsis thaliana mutants lacking the ER-PM protein tether synaptotagmin1 (SYT1) exhibit decreased plasma membrane (PM) integrity under multiple abiotic stresses such as freezing, high salt, osmotic stress and mechanical damage. Here, we show that, together with SYT1, the stress-induced SYT3 is an ER-PM tether that also functions in maintaining PM integrity. The ER-PM CS localization of SYT1 and SYT3 is dependent on PM phosphatidylinositol-4-phosphate and is regulated by abiotic stress. Lipidomic analysis revealed that cold stress increased the accumulation of diacylglycerol at the PM in a syt1/3 double mutant relative to wild type while the levels of most glycerolipid species remain unchanged. Additionally, the SYT1-green fluorescent protein (GFP) fusion preferentially binds diacylglycerol in vivo with little affinity for polar glycerolipids. Our work uncovers a SYT-dependent mechanism of stress adaptation counteracting the detrimental accumulation of diacylglycerol at the PM produced during episodes of abiotic stress.

scholarly journals Sigma 1 Receptor, Cholesterol and Endoplasmic Reticulum Contact Sites

Contact ◽  
2021 ◽  
Vol 4 ◽  
pp. 251525642110265
Author(s):  
Vladimir Zhemkov ◽  
Jen Liou ◽  
Ilya Bezprozvanny
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Composition ◽  
Sigma 1 Receptor ◽  
Functional Roles ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Sigma 1 ◽  
Membrane Contact ◽  
Organelle Communication ◽  
Cellular Organelles

Recent studies indicated potential importance of membrane contact sites (MCS) between the endoplasmic reticulum (ER) and other cellular organelles. These MCS have unique protein and lipid composition and serve as hubs for inter-organelle communication and signaling. Despite extensive investigation of MCS protein composition and functional roles, little is known about the process of MCS formation. In this perspective, we propose a hypothesis that MCS are formed not as a result of random interactions between membranes of ER and other organelles but on the basis of pre-existing cholesterol-enriched ER microdomains.

scholarly journals Ultrastructural Characterization of Flashing Mitochondria

Contact ◽  
2018 ◽  
Vol 1 ◽  
pp. 251525641880142
Author(s):  
Manon Rosselin ◽  
Paula Nunes-Hasler ◽  
Nicolas Demaurex
Keyword(s):  
Electron Microscopy ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Light And Electron Microscopy ◽  
Three Dimensional ◽  
Volume Ratio ◽  
Tubular Structures ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact

Mitochondria undergo spontaneous transient elevations in matrix pH associated with drops in mitochondrial membrane potential. These mitopHlashes require a functional respiratory chain and the profusion protein optic atrophy 1, but their mechanistic basis is unclear. To gain insight on the origin of these dynamic events, we resolved the ultrastructure of flashing mitochondria by correlative light and electron microscopy. HeLa cells expressing the matrix-targeted pH probe mitoSypHer were screened for mitopHlashes and fixed immediately after the occurrence of a flashing event. The cells were then processed for imaging by serial block face scanning electron microscopy using a focused ion beam to generate ∼1,200 slices of 10 nm thickness from a 28 µm × 15 µm cellular volume. Correlation of live/fixed fluorescence and electron microscopy images allowed the unambiguous identification of flashing and nonflashing mitochondria. Three-dimensional reconstruction and surface mapping revealed that each tomogram contained two flashing mitochondria of unequal sizes, one being much larger than the average mitochondrial volume. Flashing mitochondria were 10-fold larger than silent mitochondria but with a surface to volume ratio and a cristae volume similar to nonflashing mitochondria. Flashing mitochondria were connected by tubular structures, formed more membrane contact sites, and a constriction was observed at a junction between a flashing mitochondrion and a nonflashing mitochondrion. These data indicate that flashing mitochondria are structurally preserved and bioenergetically competent but form numerous membrane contact sites and are connected by tubular structures, consistent with our earlier suggestion that mitopHlashes might be triggered by the opening of fusion pores between contiguous mitochondria.

scholarly journals An Interorganellar Bidding War: Vps13 Localization by Competitive Organelle-Specific Adaptors

Contact ◽  
2018 ◽  
Vol 1 ◽  
pp. 251525641881462
Author(s):  
Samantha K. Dziurdzik ◽  
Björn D.M. Bean ◽  
Elizabeth Conibear
Keyword(s):  
Endoplasmic Reticulum ◽  
Recent Work ◽  
Protein Sorting ◽  
Repeat Region ◽  
Vacuolar Protein Sorting ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Prospore Membrane ◽  
Membrane Contact ◽  
Vacuolar Protein

Membrane contact sites are regulated through the controlled recruitment of constituent proteins. Yeast vacuolar protein sorting 13 (Vps13) dynamically localizes to membrane contact sites at endosomes, vacuoles, mitochondria, and the endoplasmic reticulum under different cellular conditions and is recruited to the prospore membrane during meiosis. Prior to our recent work, the mechanism for localization at contact sites was largely unknown. We identified Ypt35 as a novel Vps13 adaptor for endosomes and the nucleus-vacuole junction. Furthermore, we discovered a conserved recruitment motif in Ypt35 and found related motifs in the prospore membrane and mitochondrial adaptors, Spo71 and Mcp1, respectively. All three adaptors compete for binding to a six-repeat region of Vps13, suggesting adaptor competition regulates Vps13 localization. Here, we summarize and discuss the implications of our work, highlighting key outstanding questions.

scholarly journals Mitochondria Endoplasmic Reticulum Contact Sites (MERCs): Proximity Ligation Assay as a Tool to Study Organelle Interaction

2021 ◽  
Vol 9 ◽  
Author(s):  
Sara Benhammouda ◽  
Anjali Vishwakarma ◽  
Priya Gatti ◽  
Marc Germain
Keyword(s):  
Endoplasmic Reticulum ◽  
Fluorescence Probes ◽  
Proximity Ligation Assay ◽  
Proximity Ligation ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Endogenous Proteins ◽  
Underlying Mechanisms

Organelles cooperate with each other to regulate vital cellular homoeostatic functions. This occurs through the formation of close connections through membrane contact sites. Mitochondria-Endoplasmic-Reticulum (ER) contact sites (MERCS) are one of such contact sites that regulate numerous biological processes by controlling calcium and metabolic homeostasis. However, the extent to which contact sites shape cellular biology and the underlying mechanisms remain to be fully elucidated. A number of biochemical and imaging approaches have been established to address these questions, resulting in the identification of a number of molecular tethers between mitochondria and the ER. Among these techniques, fluorescence-based imaging is widely used, including analysing signal overlap between two organelles and more selective techniques such as in-situ proximity ligation assay (PLA). While these two techniques allow the detection of endogenous proteins, preventing some problems associated with techniques relying on overexpression (FRET, split fluorescence probes), they come with their own issues. In addition, proper image analysis is required to minimise potential artefacts associated with these methods. In this review, we discuss the protocols and outline the limitations of fluorescence-based approaches used to assess MERCs using endogenous proteins.

scholarly journals Cellular senescence links mitochondria-ER contacts and aging

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Dorian V. Ziegler ◽  
Nadine Martin ◽  
David Bernard
Keyword(s):  
Endoplasmic Reticulum ◽  
Cellular Senescence ◽  
Cellular Mechanisms ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Recent Advances ◽  
Key Players ◽  
Membrane Contact

AbstractMembrane contact sites emerged in the last decade as key players in the integration, regulation and transmission of many signals within cells, with critical impact in multiple pathophysiological contexts. Numerous studies accordingly point to a role for mitochondria-endoplasmic reticulum contacts (MERCs) in modulating aging. Nonetheless, the driving cellular mechanisms behind this role remain unclear. Recent evidence unravelled that MERCs regulate cellular senescence, a state of permanent proliferation arrest associated with a pro-inflammatory secretome, which could mediate MERC impact on aging. Here we discuss this idea in light of recent advances supporting an interplay between MERCs, cellular senescence and aging.

scholarly journals STARD 3 mediates endoplasmic reticulum‐to‐endosome cholesterol transport at membrane contact sites

2017 ◽  
Vol 36 (10) ◽  
pp. 1412-1433 ◽  
Author(s):  
Léa P Wilhelm ◽  
Corinne Wendling ◽  
Benoît Védie ◽  
Toshihide Kobayashi ◽  
Marie‐Pierre Chenard ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cholesterol Transport ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact

scholarly journals Kv2 potassium channels form endoplasmic reticulum/plasma membrane junctions via interaction with VAPA and VAPB

2018 ◽  
Vol 115 (31) ◽  
pp. E7331-E7340 ◽  
Author(s):  
Ben Johnson ◽  
Ashley N. Leek ◽  
Laura Solé ◽  
Emily E. Maverick ◽  
Tim P. Levine ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Membrane Trafficking ◽  
Neuronal Cultures ◽  
Physical Relationship ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Hek Cells ◽  
C Terminus ◽  
Membrane Contact

Kv2.1 exhibits two distinct forms of localization patterns on the neuronal plasma membrane: One population is freely diffusive and regulates electrical activity via voltage-dependent K+ conductance while a second one localizes to micrometer-sized clusters that contain densely packed, but nonconducting, channels. We have previously established that these clusters represent endoplasmic reticulum/plasma membrane (ER/PM) junctions that function as membrane trafficking hubs and that Kv2.1 plays a structural role in forming these membrane contact sites in both primary neuronal cultures and transfected HEK cells. Clustering and the formation of ER/PM contacts are regulated by phosphorylation within the channel C terminus, offering cells fast, dynamic control over the physical relationship between the cortical ER and PM. The present study addresses the mechanisms by which Kv2.1 and the related Kv2.2 channel interact with the ER membrane. Using proximity-based biotinylation techniques in transfected HEK cells we identified ER VAMP-associated proteins (VAPs) as potential Kv2.1 interactors. Confirmation that Kv2.1 and -2.2 bind VAPA and VAPB employed colocalization/redistribution, siRNA knockdown, and Förster resonance energy transfer (FRET)-based assays. CD4 chimeras containing sequence from the Kv2.1 C terminus were used to identify a noncanonical VAP-binding motif. VAPs were first identified as proteins required for neurotransmitter release in Aplysia and are now known to be abundant scaffolding proteins involved in membrane contact site formation throughout the ER. The VAP interactome includes AKAPs, kinases, membrane trafficking machinery, and proteins regulating nonvesicular lipid transport from the ER to the PM. Therefore, the Kv2-induced VAP concentration at ER/PM contact sites is predicted to have wide-ranging effects on neuronal cell biology.

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