New molecular mechanisms of inter-organelle lipid transport

2016 ◽  
Vol 44 (2) ◽  
pp. 486-492 ◽  
Author(s):  
Guillaume Drin ◽  
Joachim Moser von Filseck ◽  
Alenka Čopič
Keyword(s):  
Molecular Mechanisms ◽  
Lipid Binding ◽  
Phosphoinositide Metabolism ◽  
Lipid Transfer ◽  
Cellular Lipid ◽  
Transport Pathways ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Associated Proteins ◽  
Phosphatidylinositol 4

Lipids are precisely distributed in cell membranes, along with associated proteins defining organelle identity. Because the major cellular lipid factory is the endoplasmic reticulum (ER), a key issue is to understand how various lipids are subsequently delivered to other compartments by vesicular and non-vesicular transport pathways. Efforts are currently made to decipher how lipid transfer proteins (LTPs) work either across long distances or confined to membrane contact sites (MCSs) where two organelles are at close proximity. Recent findings reveal that proteins of the oxysterol-binding protein related-proteins (ORP)/oxysterol-binding homology (Osh) family are not all just sterol transporters/sensors: some can bind either phosphatidylinositol 4-phosphate (PtdIns(4)P) and sterol or PtdIns(4)P and phosphatidylserine (PS), exchange these lipids between membranes, and thereby use phosphoinositide metabolism to create cellular lipid gradients. Lipid exchange is likely a widespread mechanism also utilized by other LTPs to efficiently trade lipids between organelle membranes. Finally, the discovery of more proteins bearing a lipid-binding module (SMP or START-like domain) raises new questions on how lipids are conveyed in cells and how the activities of different LTPs are coordinated.

scholarly journals ORP5 and ORP8: Sterol Sensors and Phospholipid Transfer Proteins at Membrane Contact Sites?

Biomolecules ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 928
Author(s):  
Nina Criado Santos ◽  
Vladimir Girik ◽  
Paula Nunes-Hasler
Keyword(s):  
Structural Similarity ◽  
Lipid Transfer ◽  
Cellular Functions ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Phospholipid Transfer ◽  
Membrane Contact ◽  
And Migration ◽  
Phosphatidylinositol 4

Oxysterol binding related proteins 5 and 8 (ORP5 and ORP8) are two close homologs of the larger oxysterol binding protein (OSBP) family of sterol sensors and lipid transfer proteins (LTP). Early studies indicated these transmembrane proteins, anchored to the endoplasmic reticulum (ER), bound and sensed cholesterol and oxysterols. They were identified as important for diverse cellular functions including sterol homeostasis, vesicular trafficking, proliferation and migration. In addition, they were implicated in lipid-related diseases such as atherosclerosis and diabetes, but also cancer, although their mechanisms of action remained poorly understood. Then, alongside the increasing recognition that membrane contact sites (MCS) serve as hubs for non-vesicular lipid transfer, added to their structural similarity to other LTPs, came discoveries showing that ORP5 and 8 were in fact phospholipid transfer proteins that rather sense and exchange phosphatidylserine (PS) for phosphoinositides, including phosphatidylinositol-4-phosphate (PI(4)P) and potentially phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2). Evidence now points to their action at MCS between the ER and various organelles including the plasma membrane, lysosomes, mitochondria, and lipid droplets. Dissecting exactly how this unexpected phospholipid transfer function connects with sterol regulation in health or disease remains a challenge for future studies.

scholarly journals Molecular and cellular dissection of the oxysterol-binding protein cycle through a fluorescent inhibitor

2020 ◽  
Vol 295 (13) ◽  
pp. 4277-4288 ◽  
Author(s):  
Tiphaine Péresse ◽  
David Kovacs ◽  
Mélody Subra ◽  
Joëlle Bigay ◽  
Meng-Chen Tsai ◽  
...  
Keyword(s):  
Binding Protein ◽  
Lipid Binding ◽  
Lipid Transfer ◽  
Intracellular Lipid ◽  
Membrane Reconstitution ◽  
Bioactive Natural Products ◽  
Oxysterol Binding Protein ◽  
Binding Cavity ◽  
Phosphatidylinositol 4

ORPphilins are bioactive natural products that strongly and selectively inhibit the growth of some cancer cell lines and are proposed to target intracellular lipid-transfer proteins of the oxysterol-binding protein (OSBP) family. These conserved proteins exchange key lipids, such as cholesterol and phosphatidylinositol 4-phosphate (PI(4)P), between organelle membranes. Among ORPphilins, molecules of the schweinfurthin family interfere with intracellular lipid distribution and metabolism, but their functioning at the molecular level is poorly understood. We report here that cell line sensitivity to schweinfurthin G (SWG) is inversely proportional to cellular OSBP levels. By taking advantage of the intrinsic fluorescence of SWG, we followed its fate in cell cultures and show that its incorporation at the trans-Golgi network depends on cellular abundance of OSBP. Using in vitro membrane reconstitution systems and cellular imaging approaches, we also report that SWG inhibits specifically the lipid transfer activity of OSBP. As a consequence, post-Golgi trafficking, membrane cholesterol levels, and PI(4)P turnover were affected. Finally, using intermolecular FRET analysis, we demonstrate that SWG directly binds to the lipid-binding cavity of OSBP. Collectively these results describe SWG as a specific and intrinsically fluorescent pharmacological tool for dissecting OSBP properties at the cellular and molecular levels. Our findings indicate that SWG binds OSBP with nanomolar affinity, that this binding is sensitive to the membrane environment, and that SWG inhibits the OSBP-catalyzed lipid exchange cycle.

scholarly journals ORP1L mediated PI(4)P signaling at ER-lysosome-mitochondrion three-way contact contributes to mitochondrial division

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Maxime Boutry ◽  
Peter K. Kim
Keyword(s):  
Lipid Transfer Protein ◽  
Super Resolution ◽  
Lipid Transfer ◽  
Direct Role ◽  
Mitochondrial Division ◽  
Transfer Protein ◽  
Division Site ◽  
Associated Proteins ◽  
Division Process ◽  
Phosphatidylinositol 4

AbstractMitochondrial division is not an autonomous event but involves multiple organelles, including the endoplasmic reticulum (ER) and lysosomes. Whereas the ER drives the constriction of mitochondrial membranes, the role of lysosomes in mitochondrial division is not known. Here, using super-resolution live-cell imaging, we investigate the recruitment of lysosomes to the site of mitochondrial division. We find that the ER recruits lysosomes to the site of division through the interaction of VAMP-associated proteins (VAPs) with the lysosomal lipid transfer protein ORP1L to induce a three-way contact between the ER, lysosome, and the mitochondrion. We also show that ORP1L might transport phosphatidylinositol-4-phosphate (PI(4)P) from lysosomes to mitochondria, as inhibiting its transfer or depleting PI(4)P at the mitochondrial division site impairs fission, demonstrating a direct role for PI(4)P in the division process. Our findings support a model where the ER recruits lysosomes to act in concert at the fission site for the efficient division of mitochondria.

scholarly journals Functional analyses of phosphatidylserine/PI(4)P exchangers with diverse lipid species and membrane contexts set unanticipated rules on lipid transfer

2021 ◽  
Author(s):  
Souade Ikhlef ◽  
Nicolas-Frédéric Lipp ◽  
Vanessa Delfosse ◽  
Nicolas Fuggetta ◽  
William Bourguet ◽  
...  
Keyword(s):  
Lipid Transfer ◽  
Oxysterol Binding Protein ◽  
Lipid Exchange ◽  
Exchange Processes ◽  
Lipid Species ◽  
Acyl Chains ◽  
Phosphatidylinositol 4 ◽  
Functional Analyses ◽  
Related Proteins

Several members of the oxysterol-binding protein-related proteins (ORPs)/oxysterol-binding homology (Osh) family exchange phosphatidylserine (PS) and phosphatidylinositol 4-phosphate (PI(4)P) at the endoplasmic reticulum/plasma membrane (PM) interface. It is unclear whether they preferentially exchange PS and PI(4)P with specific acyl chains to tune the features of the PM, whether they use phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) instead of PI(4)P for exchange processes and whether their activity is influenced by the association of PS with sterol in the PM. Here, we measured in vitro how the yeast Osh6p and human ORP8 transported diverse PS and PI(4)P subspecies, including major cellular species, between membranes. We established how their activity is impacted by the length and unsaturation degree of these lipids. Surprisingly, the speed at which they individually transfer these ligands inversely depends on their affinity for them. To be fast, the transfer of high-affinity ligands requires an exchange with a counterligand of equivalent affinity. Besides, we determined that Osh6p and ORP8 cannot use PI(4,5)P2 for intracellular lipid exchange, as they have a low affinity for this lipid compared to PI(4)P, and do not transfer more PS into sterol-rich membranes. This study provides insights into PS/PI(4)P exchangers and sets unanticipated rules on how the activity of lipid transfer proteins relates to their affinity for ligands.

scholarly journals The structure and flexibility analysis of the Arabidopsis Synaptotagmin 1 reveal the basis of its regulation at membrane contact sites

2021 ◽  
Author(s):  
Juan Luis Benavente ◽  
Dritan Siliqi ◽  
Lourdes Infantes ◽  
Laura Lagartera ◽  
Alberto Mills ◽  
...  
Keyword(s):  
Cell Function ◽  
Lipid Extraction ◽  
Membrane Lipid ◽  
Lipid Binding ◽  
Lipid Transfer ◽  
C2 Domains ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Cellular Environment ◽  
Synaptotagmin 1

Cell function requires the maintenance of membrane lipid homeostasis as changes in cellular environment unbalance this equilibrium. The non-vesicular lipid transfer at endoplasmic reticulum (ER) and plasma membrane (PM) contact sites (CS) is central to restore it. Extended synaptotagmins (E-Syts) are ER proteins that play a central role in this process as they act as molecular tethers with PM and as lipid transfer proteins between these organelles. E-Syts are constitutively anchored to the ER through an N-terminal hydrophobic segment and bind to the PM via C-terminal C2 domains. In plants, synaptotagmins (SYTs) are orthologous of E-Syts and regulate the ER-PM communication by the activity of their two C2 domains in response to abiotic stresses. We have combined macromolecular crystallography, small-angle X-ray scattering, structural bioinformatics and biochemical data to analyze the regulation of plant synaptotagmin 1 (SYT1). Our data show that the binding of SYT1 to the PM is regulated by the interaction of the first C2 domain through a Ca2+-dependent lipid binding site and by a site for phosphorylated forms of phosphatidylinositol in such a way that two different molecular signals are integrated in response to stress. In addition, our data show that SYT1 is highly flexible by virtue of up to three hinge points, including one that connects the two C2 domains. This feature provides conformational freedom to SYT1 to define a large and complementary interaction surface with the PM. This structural plasticity, in turn, may facilitate lipid extraction, protein loading and subsequent transfer between PM and ER.

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 The oxysterol-binding protein superfamily: new concepts and old proteins

2012 ◽  
Vol 40 (2) ◽  
pp. 469-473 ◽  
Author(s):  
Michelle L. Villasmil ◽  
Vytas A. Bankaitis ◽  
Carl J. Mousley
Keyword(s):  
Lipid Metabolism ◽  
Membrane Trafficking ◽  
Transcriptional Control ◽  
Binding Protein ◽  
Lipid Binding ◽  
Oxysterol Binding Protein ◽  
New Concepts ◽  
Endosomal Membranes ◽  
Phosphatidylinositol 4 ◽  
Golgi Network

The Kes1 OSBP (oxysterol-binding protein) is a key regulator of membrane trafficking through the TGN (trans-Golgi network) and endosomal membranes. We demonstrated recently that Kes1 acts as a sterol-regulated rheostat for TGN/endosomal phosphatidylinositol 4-phosphate signalling. Kes1 utilizes its dual lipid-binding activities to integrate endosomal lipid metabolism with TORC1 (target of rapamycin complex 1)-dependent proliferative pathways and transcriptional control of nutrient signalling.

Building lipid ‘PIPelines’ throughout the cell by ORP/Osh proteins

2014 ◽  
Vol 42 (5) ◽  
pp. 1465-1470 ◽  
Author(s):  
Joachim Moser von Filseck ◽  
Bruno Mesmin ◽  
Joëlle Bigay ◽  
Bruno Antonny ◽  
Guillaume Drin
Keyword(s):  
Secretory Pathway ◽  
Eukaryotic Cells ◽  
Transport Mechanisms ◽  
Related Protein ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Species ◽  
Membrane Contact ◽  
Phosphatidylinositol 4

In eukaryotic cells, a sterol gradient exists between the early and late regions of the secretory pathway. This gradient seems to rely on non-vesicular transport mechanisms mediated by specialized carriers. The oxysterol-binding protein-related protein (ORP)/oxysterol-binding homology (Osh) family has been assumed initially to exclusively include proteins acting as sterol sensors/transporters and many efforts have been made to determine their mode of action. Our recent studies have demonstrated that some ORP/Osh proteins are not mere sterol transporters, but sterol/phosphatidylinositol 4-phosphate [PI(4)P] exchangers. They exploit the PI(4)P gradient at the endoplasmic reticulum (ER)/Golgi interface, or at membrane-contact sites between these compartments, to actively create a sterol gradient. Other recent reports have suggested that all ORP/Osh proteins bind PI(4)P and recognize a second lipid that is not necessary sterol. We have thus proposed that ORP/Osh proteins use PI(4)P gradients between organelles to convey various lipid species.

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 Transport Pathways That Contribute to the Cellular Distribution of Phosphatidylserine

2021 ◽  
Vol 9 ◽  
Author(s):  
Guillaume Lenoir ◽  
Juan Martín D’Ambrosio ◽  
Thibaud Dieudonné ◽  
Alenka Čopič
Keyword(s):  
Structural Data ◽  
Cellular Distribution ◽  
Lipid Transfer ◽  
Lipid Transfer Proteins ◽  
Transport Pathways ◽  
Flip Flop ◽  
Membrane Contact Sites ◽  
Passive Flow ◽  
Combined Action ◽  
Membrane Contact

Phosphatidylserine (PS) is a negatively charged phospholipid that displays a highly uneven distribution within cellular membranes, essential for establishment of cell polarity and other processes. In this review, we discuss how combined action of PS biosynthesis enzymes in the endoplasmic reticulum (ER), lipid transfer proteins (LTPs) acting within membrane contact sites (MCS) between the ER and other compartments, and lipid flippases and scramblases that mediate PS flip-flop between membrane leaflets controls the cellular distribution of PS. Enrichment of PS in specific compartments, in particular in the cytosolic leaflet of the plasma membrane (PM), requires input of energy, which can be supplied in the form of ATP or by phosphoinositides. Conversely, coupling between PS synthesis or degradation, PS flip-flop and PS transfer may enable PS transfer by passive flow. Such scenario is best documented by recent work on the formation of autophagosomes. The existence of lateral PS nanodomains, which is well-documented in the case of the PM and postulated for other compartments, can change the steepness or direction of PS gradients between compartments. Improvements in cellular imaging of lipids and membranes, lipidomic analysis of complex cellular samples, reconstitution of cellular lipid transport reactions and high-resolution structural data have greatly increased our understanding of cellular PS homeostasis. Our review also highlights how budding yeast has been instrumental for our understanding of the organization and transport of PS in cells.

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