scholarly journals In-vitro Reconstitution of Membrane Contact Sites between the Endoplasmic Reticulum and Lipid Droplets

2021 ◽  
Author(s):  
Sukrut Kamerkar ◽  
Jagjeet Singh ◽  
Subham Tripathy ◽  
Hemangi Bhonsle ◽  
Mukesh Kumar ◽  
...  
Keyword(s):  
Rat Liver ◽  
Lipid Droplets ◽  
Cell Function ◽  
Cultured Cells ◽  
Optical Trap ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Organelle Communication

Coordinated cell function requires inter-organelle communication across Membrane Contact Sites (MCS). Here we deposit ER-enriched microsomes purified from rat liver or from cultured cells on a coverslip in the form of a continuous planar membrane. We visualize real-time protein and lipid exchanges across MCS that form between this ER-mimicking membrane and lipid droplets purified from rat liver. An Optical trap is used to demonstrate physical tethering of individual lipid droplets to the ER-mimicking membrane at MCS, and to directly measure the strength of this tether. In-vitro MCS formation changes dramatically in response to metabolic state and immune activation in the animal. Surprisingly, we find that the Rab18 GTPase and Phosphatidic acid are common molecular factors to control both of these pathways. This assay could possibly be adapted to interrogate MCS formation between other membranes (e.g. mitochondria, peroxisomes, endosomes etc.), and abnormalities therein that cause neurological, metabolic and pathogenic diseases.

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.

The role of phosphatidylinositol-transfer proteins at membrane contact sites

2016 ◽  
Vol 44 (2) ◽  
pp. 419-424 ◽  
Author(s):  
Michael Selitrennik ◽  
Sima Lev
Keyword(s):  
Underlying Mechanism ◽  
Cellular Processes ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Compartments ◽  
Potential Mode ◽  
Membrane Contact ◽  
Phosphatidylinositol Transfer ◽  
Phosphatidylinositol Transfer Proteins

Phosphatidylinositol-transfer proteins (PITPs) have been initially identified as soluble factors that accelerate the monomeric exchange of either phosphatidylinositol (PI) or phosphatidylcholine (PC) between membrane bilayers in vitro. They are highly conserved in eukaryotes and have been implicated in different cellular processes, including vesicular trafficking, signal transduction, and lipid metabolism. Recent studies suggest that PITPs function at membrane contact sites (MCSs) to facilitate the transport of PI from its synthesis site at the endoplasmic reticulum (ER) to various membrane compartments. In this review, we describe the underlying mechanism of PITPs targeting to MCSs, discuss their cellular roles and potential mode of action.

scholarly journals Lipid transfer proteins do their thing anchored at membrane contact sites… but what is their thing?

2016 ◽  
Vol 44 (2) ◽  
pp. 517-527 ◽  
Author(s):  
Louise H. Wong ◽  
Tim P. Levine
Keyword(s):  
Lipid Binding ◽  
Lipid Transfer ◽  
Transmembrane Helices ◽  
Lipid Transfer Proteins ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Multiple Contacts ◽  
Membrane Contact ◽  
Organelle Communication ◽  
Lipid Binding Proteins

Membrane contact sites are structures where two organelles come close together to regulate flow of material and information between them. One type of inter-organelle communication is lipid exchange, which must occur for membrane maintenance and in response to environmental and cellular stimuli. Soluble lipid transfer proteins have been extensively studied, but additional families of transfer proteins have been identified that are anchored into membranes by transmembrane helices so that they cannot diffuse through the cytosol to deliver lipids. If such proteins target membrane contact sites they may be major players in lipid metabolism. The eukaryotic family of so-called Lipid transfer proteins Anchored at Membrane contact sites (LAMs) all contain both a sterol-specific lipid transfer domain in the StARkin superfamily (related to StART/Bet_v1), and one or more transmembrane helices anchoring them in the endoplasmic reticulum (ER), making them interesting subjects for study in relation to sterol metabolism. They target a variety of membrane contact sites, including newly described contacts between organelles that were already known to make contact by other means. Lam1–4p target punctate ER–plasma membrane contacts. Lam5p and Lam6p target multiple contacts including a new category: vacuolar non-NVJ cytoplasmic ER (VancE) contacts. These developments confirm previous observations on tubular lipid-binding proteins (TULIPs) that established the importance of membrane anchored proteins for lipid traffic. However, the question remaining to be solved is the most difficult of all: are LAMs transporters, or alternately are they regulators that affect traffic more indirectly?

scholarly journals Nanoscale architecture of a VAP-A-OSBP tethering complex at membrane contact sites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Eugenio de la Mora ◽  
Manuela Dezi ◽  
Aurélie Di Cicco ◽  
Joëlle Bigay ◽  
Romain Gautier ◽  
...  
Keyword(s):  
Lipid Transfer Protein ◽  
Structural Information ◽  
Transmembrane Protein ◽  
Lipid Transfer ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Golgi Network

AbstractMembrane contact sites (MCS) are subcellular regions where two organelles appose their membranes to exchange small molecules, including lipids. Structural information on how proteins form MCS is scarce. We designed an in vitro MCS with two membranes and a pair of tethering proteins suitable for cryo-tomography analysis. It includes VAP-A, an ER transmembrane protein interacting with a myriad of cytosolic proteins, and oxysterol-binding protein (OSBP), a lipid transfer protein that transports cholesterol from the ER to the trans Golgi network. We show that VAP-A is a highly flexible protein, allowing formation of MCS of variable intermembrane distance. The tethering part of OSBP contains a central, dimeric, and helical T-shape region. We propose that the molecular flexibility of VAP-A enables the recruitment of partners of different sizes within MCS of adjustable thickness, whereas the T geometry of the OSBP dimer facilitates the movement of the two lipid-transfer domains between membranes.

scholarly journals Peroxisomal Membrane Contact Sites in Yeasts

2021 ◽  
Vol 9 ◽  
Author(s):  
Amit S. Joshi
Keyword(s):  
Lipid Droplets ◽  
Peroxisome Biogenesis ◽  
Functional Importance ◽  
Peroxisomal Membrane ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Recent Developments ◽  
Membrane Contacts ◽  
Membrane Bound ◽  
Membrane Contact

Peroxisomes are ubiquitous, single membrane-bound organelles that play a crucial role in lipid metabolism and human health. While peroxisome number is maintained by the division of existing peroxisomes, nascent peroxisomes can be generated from the endoplasmic reticulum (ER) membrane in yeasts. During formation and proliferation, peroxisomes maintain membrane contacts with the ER. In addition to the ER, contacts between peroxisomes and other organelles such as lipid droplets, mitochondria, vacuole, and plasma membrane have been reported. These membrane contact sites (MCS) are dynamic and important for cellular function. This review focuses on the recent developments in peroxisome biogenesis and the functional importance of peroxisomal MCS in yeasts.

PI4P/PS countertransport by ORP10 at ER–endosome membrane contact sites regulates endosome fission

2021 ◽  
Vol 221 (1) ◽  
Author(s):  
Asami Kawasaki ◽  
Akiko Sakai ◽  
Hiroki Nakanishi ◽  
Junya Hasegawa ◽  
Tomohiko Taguchi ◽  
...  
Keyword(s):  
Membrane Trafficking ◽  
Binding Protein ◽  
Dependent Manner ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Exchange ◽  
Membrane Contact ◽  
Phosphatidylinositol 4

Membrane contact sites (MCSs) serve as a zone for nonvesicular lipid transport by oxysterol-binding protein (OSBP)-related proteins (ORPs). ORPs mediate lipid countertransport, in which two distinct lipids are transported counterdirectionally. How such lipid countertransport controls specific biological functions, however, remains elusive. We report that lipid countertransport by ORP10 at ER–endosome MCSs regulates retrograde membrane trafficking. ORP10, together with ORP9 and VAP, formed ER–endosome MCSs in a phosphatidylinositol 4-phosphate (PI4P)-dependent manner. ORP10 exhibited a lipid exchange activity toward its ligands, PI4P and phosphatidylserine (PS), between liposomes in vitro, and between the ER and endosomes in situ. Cell biological analysis demonstrated that ORP10 supplies a pool of PS from the ER, in exchange for PI4P, to endosomes where the PS-binding protein EHD1 is recruited to facilitate endosome fission. Our study highlights a novel lipid exchange at ER–endosome MCSs as a nonenzymatic PI4P-to-PS conversion mechanism that organizes membrane remodeling during retrograde membrane trafficking.

scholarly journals Getting a handle on lipid droplets: Insights into ER–lipid droplet tethering

2019 ◽  
Vol 218 (4) ◽  
pp. 1089-1091 ◽  
Author(s):  
Truc B. Nguyen ◽  
James A. Olzmann
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Human Cells ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Cell Biol ◽  
Membrane Contact

Lipid droplets (LDs) are hubs for lipid metabolism that form membrane contact sites with multiple organelles. In this issue, Hariri et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808119) reveal the functions of Mdm1-mediated endoplasmic reticulum (ER)–LD tethering in yeast and Datta et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808133) identify a role for the Mdm1 orthologue, Snx14, as an ER–LD tether that regulates lipid metabolism in human cells.

scholarly journals Perspectives on Mitochondria–ER and Mitochondria–Lipid Droplet Contact in Hepatocytes and Hepatic Lipid Metabolism

Cells ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 2273
Author(s):  
Xiaowen Ma ◽  
Hui Qian ◽  
Allen Chen ◽  
Hong-Min Ni ◽  
Wen-Xing Ding
Keyword(s):  
Lipid Metabolism ◽  
Liver Disease ◽  
Lipid Droplet ◽  
Alcoholic Fatty Liver ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Intracellular Organelles ◽  
Membrane Contact ◽  
Related Liver Disease ◽  
Organelle Communication

Emerging evidence suggests that mitochondrion–endoplasmic reticulum (ER) and mitochondrion–lipid droplet (LD) contact sites are critical in regulating lipid metabolism in cells. It is well established that intracellular organelles communicate with each other continuously through membrane contact sites to maintain organelle function and cellular homeostasis. The accumulation of LDs in hepatocytes is an early indicator of non-alcoholic fatty liver disease (NAFLD) and alcohol-related liver disease (ALD), which may indicate a breakdown in proper inter-organelle communication. In this review, we discuss previous findings in mitochondrion–ER and mitochondrion–LD contact, focusing on their roles in lipid metabolism in hepatocytes. We also present evidence of a unique mitochondrion–LD contact structure in hepatocytes under various physiological and pathological conditions and propose a working hypothesis to speculate about the role of these structures in regulating the functions of mitochondria and LDs and their implications in NAFLD and ALD.

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