scholarly journals Mdm1/Snx13 is a novel ER–endolysosomal interorganelle tethering protein

2015 ◽  
Vol 210 (4) ◽  
pp. 541-551 ◽  
Author(s):  
W. Mike Henne ◽  
Lu Zhu ◽  
Zsolt Balogi ◽  
Christopher Stefan ◽  
Jeffrey A. Pleiss ◽  
...  
Keyword(s):  
Neurological Disease ◽  
Lipid Binding ◽  
Sphingolipid Metabolism ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Effector Genes ◽  
Px Domain ◽  
In Trans ◽  
Membrane Contact ◽  
Lysosome Membrane

Although endolysosomal trafficking is well defined, how it is regulated and coordinates with cellular metabolism is unclear. To identify genes governing endolysosomal dynamics, we conducted a global fluorescence-based screen to reveal endomembrane effector genes. Screening implicated Phox (PX) domain–containing protein Mdm1 in endomembrane dynamics. Surprisingly, we demonstrate that Mdm1 is a novel interorganelle tethering protein that localizes to endoplasmic reticulum (ER)–vacuole/lysosome membrane contact sites (MCSs). We show that Mdm1 is ER anchored and contacts the vacuole surface in trans via its lipid-binding PX domain. Strikingly, overexpression of Mdm1 induced ER–vacuole hypertethering, underscoring its role as an interorganelle tether. We also show that Mdm1 and its paralogue Ydr179w-a (named Nvj3 in this study) localize to ER–vacuole MCSs independently of established tether Nvj1. Finally, we find that Mdm1 truncations analogous to neurological disease–associated SNX14 alleles fail to tether the ER and vacuole and perturb sphingolipid metabolism. Our work suggests that human Mdm1 homologues may play previously unappreciated roles in interorganelle communication and lipid metabolism.

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 SAC1 Degrades its Lipid Substrate PtdIns4P in the Endoplasmic Reticulum to Maintain a Steep Chemical Gradient with Donor Membranes

2018 ◽  
Author(s):  
James P. Zewe ◽  
Rachel C. Wills ◽  
Sahana Sangappa ◽  
Brady D. Goulden ◽  
Gerald R. V. Hammond
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Homeostasis ◽  
Chemical Gradient ◽  
Vesicular Traffic ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Catalytic Domains ◽  
In Trans ◽  
Membrane Contact ◽  
And Function

AbstractGradients of PtdIns4P between organelle membranes and the endoplasmic reticulum (ER) are thought to drive counter-transport of other lipids via non-vesicular traffic. This novel pathway requires the SAC1 phosphatase to degrade PtdIns4P in a “cis” configuration at the ER to maintain the gradient. However, SAC1 has also been proposed to act in “trans” at membrane contact sites, which could oppose lipid traffic. It is therefore crucial to determine which mode SAC1 uses in living cells. We report that acute inhibition of SAC1 causes accumulation of PtdIns4P in the ER, that SAC1 does not enrich at membrane contact sites, and that SAC1 has little activity in “trans”, unless a linker is added between its ER-anchored and catalytic domains. The data reveal an obligate “cis” activity of SAC1, supporting its role in non-vesicular lipid traffic and implicating lipid traffic more broadly in inositol lipid homeostasis and function.

scholarly journals CRISPR screens for lipid regulators reveal a role for ER-bound SNX13 in lysosomal cholesterol export

2021 ◽  
Vol 221 (2) ◽  
Author(s):  
Albert Lu ◽  
Frank Hsieh ◽  
Bikal R. Sharma ◽  
Sydney R. Vaughn ◽  
Carlos Enrich ◽  
...  
Keyword(s):  
Lipid Droplet ◽  
Negative Regulator ◽  
Gene Products ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Genome Wide ◽  
Lipid Regulators ◽  
Membrane Contact ◽  
Lysosome Membrane ◽  
Insight Into

We report here two genome-wide CRISPR screens performed to identify genes that, when knocked out, alter levels of lysosomal cholesterol or bis(monoacylglycero)phosphate. In addition, these screens were also performed under conditions of NPC1 inhibition to identify modifiers of NPC1 function in lysosomal cholesterol export. The screens confirm tight coregulation of cholesterol and bis(monoacylglycero)phosphate in cells and reveal an unexpected role for the ER-localized SNX13 protein as a negative regulator of lysosomal cholesterol export and contributor to ER–lysosome membrane contact sites. In the absence of NPC1 function, SNX13 knockdown redistributes lysosomal cholesterol and is accompanied by triacylglycerol-rich lipid droplet accumulation and increased lysosomal bis(monoacylglycero)phosphate. These experiments provide unexpected insight into the regulation of lysosomal lipids and modification of these processes by novel gene products.

ER-Golgi membrane contact sites

2020 ◽  
Vol 48 (1) ◽  
pp. 187-197 ◽  
Author(s):  
Rossella Venditti ◽  
Maria Chiara Masone ◽  
Maria Antonietta De Matteis
Keyword(s):  
Lipid Transfer ◽  
Lipid Transfer Proteins ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Exchange ◽  
Pathological Conditions ◽  
The Sixties ◽  
In Trans ◽  
Membrane Contact ◽  
Methodological Approaches

Membrane contact sites (MCSs) are sites where the membranes of two different organelles come into close apposition (10–30 nm). Different classes of proteins populate MCSs including factors that act as tethers between the two membranes, proteins that use the MCSs for their function (mainly lipid or ion exchange), and regulatory proteins and enzymes that can act in trans across the MCSs. The ER-Golgi MCSs were visualized by electron microscopists early in the sixties but have remained elusive for decades due to a lack of suitable methodological approaches. Here we report recent progress in the study of this class of MCSs that has led to the identification of their main morphological features and of some of their components and roles. Among these, lipid transfer proteins and lipid exchange have been the most studied and understood so far. However, many unknowns remain regarding their regulation and their role in controlling key TGN functions such as sorting and trafficking as well as their relevance in physiological and pathological conditions.

scholarly journals The Hob proteins are novel and conserved lipid binding proteins at ER-PM contact sites

2021 ◽  
Author(s):  
Sarah D. Neuman ◽  
Jeff R. Jorgensen ◽  
Amy T. Cavanagh ◽  
Jeremy T. Smyth ◽  
Jane E. Selegue ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Protein Composition ◽  
Lipid Binding ◽  
Model Systems ◽  
Yeast Cells ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Critical Junctures ◽  
C Terminus ◽  
Membrane Contact

ABSTRACTMembrane contact sites are critical junctures for organelle signaling and communication. Endoplasmic reticulum-plasma membrane (ER-PM) contact sites were the first membrane contact sites to be described; however, the protein composition and molecular function of these sites is still emerging. Here, we leverage yeast and Drosophila model systems to uncover a novel role for the Hobbit/Hob proteins at ER-PM contact sites. We find that Hobbit localizes to ER-PM contact sites in both yeast cells and the Drosophila larval salivary glands, and this localization is mediated by an N-terminal ER membrane anchor and conserved C-terminal sequences. The C-terminus of Hobbit binds to plasma membrane phosphatidylinositols, and the distribution of these lipids is altered in hobbit mutant cells. Notably, the Hobbit protein is essential for viability in higher animals, providing one of the first examples of a membrane contact site-localized lipid binding protein that is required for development.

scholarly journals Membrane Contact Sites in Yeast: Control Hubs of Sphingolipid Homeostasis

Membranes ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 971
Author(s):  
Philipp Schlarmann ◽  
Atsuko Ikeda ◽  
Kouichi Funato
Keyword(s):  
Plasma Membrane ◽  
Intracellular Signaling ◽  
Membrane Lipids ◽  
Sphingolipid Metabolism ◽  
Yeast Saccharomyces Cerevisiae ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
And Function

Sphingolipids are the most diverse class of membrane lipids, in terms of their structure and function. Structurally simple sphingolipid precursors, such as ceramides, act as intracellular signaling molecules in various processes, including apoptosis, whereas mature and complex forms of sphingolipids are important structural components of the plasma membrane. Supplying complex sphingolipids to the plasma membrane, according to need, while keeping pro-apoptotic ceramides in check is an intricate task for the cell and requires mechanisms that tightly control sphingolipid synthesis, breakdown, and storage. As each of these processes takes place in different organelles, recent studies, using the budding yeast Saccharomyces cerevisiae, have investigated the role of membrane contact sites as hubs that integrate inter-organellar sphingolipid transport and regulation. In this review, we provide a detailed overview of the findings of these studies and put them into the context of established regulatory mechanisms of sphingolipid homeostasis. We have focused on the role of membrane contact sites in sphingolipid metabolism and ceramide transport, as well as the mechanisms that prevent toxic ceramide accumulation.

scholarly journals SAC1 degrades its lipid substrate PtdIns4P in the endoplasmic reticulum to maintain a steep chemical gradient with donor membranes

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
James P Zewe ◽  
Rachel C Wills ◽  
Sahana Sangappa ◽  
Brady D Goulden ◽  
Gerald RV Hammond
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Homeostasis ◽  
Chemical Gradient ◽  
Vesicular Traffic ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Catalytic Domains ◽  
In Trans ◽  
Membrane Contact ◽  
And Function

Gradients of PtdIns4P between organelle membranes and the endoplasmic reticulum (ER) are thought to drive counter-transport of other lipids via non-vesicular traffic. This novel pathway requires the SAC1 phosphatase to degrade PtdIns4P in a ‘cis’ configuration at the ER to maintain the gradient. However, SAC1 has also been proposed to act in ‘trans’ at membrane contact sites, which could oppose lipid traffic. It is therefore crucial to determine which mode SAC1 uses in living cells. We report that acute inhibition of SAC1 causes accumulation of PtdIns4P in the ER, that SAC1 does not enrich at membrane contact sites, and that SAC1 has little activity in ‘trans’, unless a linker is added between its ER-anchored and catalytic domains. The data reveal an obligate ‘cis’ activity of SAC1, supporting its role in non-vesicular lipid traffic and implicating lipid traffic more broadly in inositol lipid homeostasis and function.

scholarly journals A new family of StART domain proteins at membrane contact sites has a role in ER-PM sterol transport

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Alberto T Gatta ◽  
Louise H Wong ◽  
Yves Y Sere ◽  
Diana M Calderón-Noreña ◽  
Shamshad Cockcroft ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Lipid Transfer ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
New Family ◽  
Sterol Transport ◽  
In Trans ◽  
Membrane Contact ◽  
Start Domain

Sterol traffic between the endoplasmic reticulum (ER) and plasma membrane (PM) is a fundamental cellular process that occurs by a poorly understood non-vesicular mechanism. We identified a novel, evolutionarily diverse family of ER membrane proteins with StART-like lipid transfer domains and studied them in yeast. StART-like domains from Ysp2p and its paralog Lam4p specifically bind sterols, and Ysp2p, Lam4p and their homologs Ysp1p and Sip3p target punctate ER-PM contact sites distinct from those occupied by known ER-PM tethers. The activity of Ysp2p, reflected in amphotericin-sensitivity assays, requires its second StART-like domain to be positioned so that it can reach across ER-PM contacts. Absence of Ysp2p, Ysp1p or Sip3p reduces the rate at which exogenously supplied sterols traffic from the PM to the ER. Our data suggest that these StART-like proteins act in trans to mediate a step in sterol exchange between the PM and ER.

scholarly journals The Hob proteins are novel and conserved lipid-binding proteins at ER–PM contact sites

2021 ◽  
Vol 135 (5) ◽  
Author(s):  
Sarah D. Neuman ◽  
Jeff R. Jorgensen ◽  
Amy T. Cavanagh ◽  
Jeremy T. Smyth ◽  
Jane E. Selegue ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Protein Composition ◽  
Lipid Binding ◽  
Model Systems ◽  
Yeast Cells ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Critical Junctures ◽  
C Terminus ◽  
Membrane Contact

ABSTRACT Membrane contact sites are critical junctures for organelle signaling and communication. Endoplasmic reticulum–plasma membrane (ER–PM) contact sites were the first membrane contact sites to be described; however, the protein composition and molecular function of these sites is still emerging. Here, we leverage yeast and Drosophila model systems to uncover a novel role for the Hobbit (Hob) proteins at ER–PM contact sites. We find that Hobbit localizes to ER–PM contact sites in both yeast cells and the Drosophila larval salivary glands, and this localization is mediated by an N-terminal ER membrane anchor and conserved C-terminal sequences. The C-terminus of Hobbit binds to plasma membrane phosphatidylinositols, and the distribution of these lipids is altered in hobbit mutant cells. Notably, the Hobbit protein is essential for viability in Drosophila, providing one of the first examples of a membrane contact site-localized lipid binding protein that is required for development.

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