Chloroplast lipid synthesis and lipid trafficking through ER–plastid membrane contact sites

2012 ◽  
Vol 40 (2) ◽  
pp. 457-463 ◽  
Author(s):  
Zhen Wang ◽  
Christoph Benning
Keyword(s):  
Fatty Acids ◽  
Current Knowledge ◽  
Lipid Transfer ◽  
Photosynthetic Membrane ◽  
Lipid Trafficking ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Envelope Membranes ◽  
Thylakoid Lipids

Plant chloroplasts contain an intricate photosynthetic membrane system, the thylakoids, and are surrounded by two envelope membranes at which thylakoid lipids are assembled. The glycoglycerolipids mono- and digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol as well as phosphatidylglycerol, are present in thylakoid membranes, giving them a unique composition. Fatty acids are synthesized in the chloroplast and are either directly assembled into thylakoid lipids at the envelope membranes or exported to the ER (endoplasmic reticulum) for extraplastidic lipid assembly. A fraction of lipid precursors is reimported into the chloroplast for the synthesis of thylakoid lipids. Thus polar lipid assembly in plants requires tight co-ordination between the chloroplast and the ER and necessitates inter-organelle lipid trafficking. In the present paper, we discuss the current knowledge of the export of fatty acids from the chloroplast and the import of chloroplast lipid precursors assembled at the ER. Direct membrane contact sites between the ER and the chloroplast outer envelopes are discussed as possible conduits for lipid transfer.

Non-vesicular lipid trafficking at the endoplasmic reticulum–mitochondria interface

2018 ◽  
Vol 46 (2) ◽  
pp. 437-452 ◽  
Author(s):  
Francesca Giordano
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Transport ◽  
Lipid Transfer ◽  
Lipid Transfer Proteins ◽  
Transport Pathways ◽  
Lipid Trafficking ◽  
Cellular Processes ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact

Mitochondria are highly dynamic organelles involved in various cellular processes such as energy production, regulation of calcium homeostasis, lipid trafficking, and apoptosis. To fulfill all these functions and preserve their morphology and dynamic behavior, mitochondria need to maintain a defined protein and lipid composition in both their membranes. The maintenance of mitochondrial membrane identity requires a selective and regulated transport of specific lipids from/to the endoplasmic reticulum (ER) and across the mitochondria outer and inner membranes. Since they are not integrated in the classical vesicular trafficking routes, mitochondria exchange lipids with the ER at sites of close apposition called membrane contact sites. Deregulation of such transport activities results in several pathologies including cancer and neurodegenerative disorders. However, we are just starting to understand the function of ER–mitochondria contact sites in lipid transport, what are the proteins involved and how they are regulated. In this review, we summarize recent insights into lipid transport pathways at the ER–mitochondria interface and discuss the implication of recently identified lipid transfer proteins in these processes.

scholarly journals The Hob Proteins: Putative, Novel Lipid Transfer Proteins at ER-PM Contact Sites

Contact ◽  
2021 ◽  
Vol 4 ◽  
pp. 251525642110523
Author(s):  
Sarah D. Neuman ◽  
Amy T. Cavanagh ◽  
Arash Bashirullah
Keyword(s):  
Structural Models ◽  
Model Systems ◽  
Lipid Transfer ◽  
Lipid Transfer Proteins ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Bona Fide ◽  
Membrane Contact ◽  
Mutant Cells ◽  
Critical Process

Nonvesicular transfer of lipids at membrane contact sites (MCS) has recently emerged as a critical process for cellular function. Lipid transfer proteins (LTPs) mediate this unique transport mechanism, and although several LTPs are known, the cellular complement of these proteins continues to expand. Our recent work has revealed the highly conserved but poorly characterized Hobbit/Hob proteins as novel, putative LTPs at endoplasmic reticulum-plasma membrane (ER-PM) contact sites. Using both S. cerevisiae and D. melanogaster model systems, we demonstrated that the Hob proteins localize to ER-PM contact sites via an N-terminal ER membrane anchor and conserved C-terminal sequences. These conserved C-terminal sequences bind to phosphoinositides (PIPs), and the distribution of PIPs is disrupted in hobbit mutant cells. Recently released structural models of the Hob proteins exhibit remarkable similarity to other bona fide LTPs, like VPS13A and ATG2, that function at MCS. Hobbit is required for viability in Drosophila, suggesting that the Hob proteins are essential genes that may mediate lipid transfer at MCS.

scholarly journals The endoplasmic reticulum-mitochondria encounter structure: coordinating lipid metabolism across membranes

2020 ◽  
Vol 401 (6-7) ◽  
pp. 811-820 ◽  
Author(s):  
Benoît Kornmann
Keyword(s):  
Endoplasmic Reticulum ◽  
Bacterial Symbiont ◽  
Exact Role ◽  
Intracellular Lipid ◽  
Lipid Trafficking ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Tethering ◽  
Membrane Contact ◽  
Insight Into

AbstractEndosymbiosis, the beginning of a collaboration between an archaeon and a bacterium and a founding step in the evolution of eukaryotes, owes its success to the establishment of communication routes between the host and the symbiont to allow the exchange of metabolites. As far as lipids are concerned, it is the host that has learnt the symbiont’s language, as eukaryote lipids appear to have been borrowed from the bacterial symbiont. Mitochondria exchange lipids with the rest of the cell at membrane contact sites. In fungi, the endoplasmic reticulum-mitochondria encounter structure (ERMES) is one of the best understood membrane tethering complexes. Its discovery has yielded crucial insight into the mechanisms of intracellular lipid trafficking. Despite a wealth of data, our understanding of ERMES formation and its exact role(s) remains incomplete. Here, I endeavour to summarise our knowledge on the ERMES complex and to identify lingering gaps.

scholarly journals Reconstitution of autophagosome nucleation defines Atg9 vesicles as seeds for membrane formation

Science ◽  
2020 ◽  
Vol 369 (6508) ◽  
pp. eaaz7714 ◽  
Author(s):  
Justyna Sawa-Makarska ◽  
Verena Baumann ◽  
Nicolas Coudevylle ◽  
Sören von Bülow ◽  
Veronika Nogellova ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
De Novo ◽  
Lipid Transfer ◽  
Related Protein ◽  
Membrane Formation ◽  
Selective Autophagy ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Phosphatidylinositol 3

Autophagosomes form de novo in a manner that is incompletely understood. Particularly enigmatic are autophagy-related protein 9 (Atg9)–containing vesicles that are required for autophagy machinery assembly but do not supply the bulk of the autophagosomal membrane. In this study, we reconstituted autophagosome nucleation using recombinant components from yeast. We found that Atg9 proteoliposomes first recruited the phosphatidylinositol 3-phosphate kinase complex, followed by Atg21, the Atg2-Atg18 lipid transfer complex, and the E3-like Atg12–Atg5-Atg16 complex, which promoted Atg8 lipidation. Furthermore, we found that Atg2 could transfer lipids for Atg8 lipidation. In selective autophagy, these reactions could potentially be coupled to the cargo via the Atg19-Atg11-Atg9 interactions. We thus propose that Atg9 vesicles form seeds that establish membrane contact sites to initiate lipid transfer from compartments such as the endoplasmic reticulum.

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 Spezifische Membrankontaktstellen bei Pflanzen: wer mit wem, warum und wie

BIOspektrum ◽  
2021 ◽  
Vol 27 (7) ◽  
pp. 693-696
Author(s):  
Anna-Lena Falz ◽  
Stefanie J. Müller-Schüssele
Keyword(s):  
Current Knowledge ◽  
Cellular Membranes ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Subcellular Compartments ◽  
Membrane Contact ◽  
Specific Pair

AbstractCellular membranes can serve as barriers between subcellular compartments, but they can also interact to form dynamically regulated membrane contact sites between a specific pair of organelles. Focussing on plants, this article discusses local redox environments and the current knowledge on membrane contact sites as examples for the dividing and connecting functions of membranes, respectively.

scholarly journals Calcium-stimulated disassembly of focal adhesions mediated by an ORP3/IQSec1 complex

2019 ◽  
Author(s):  
RS D’Souza ◽  
JY Lim ◽  
A Turgut ◽  
K Servage ◽  
J Zhang ◽  
...  
Keyword(s):  
Cell Migration ◽  
Lipid Transfer Protein ◽  
Calcium Influx ◽  
Focal Adhesions ◽  
Lipid Transfer ◽  
Transfer Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Exchange ◽  
Membrane Contact

AbstractCoordinated assembly and disassembly of integrin-mediated focal adhesions (FAs) is essential for cell migration. Many studies have shown that FA disassembly requires Ca2+ influx, however our understanding of this process remains incomplete. Here we show that Ca2+ influx via STIM1/Orai1 calcium channels, which cluster near FAs, leads to activation of the GTPase Arf5 via the Ca2+-activated GEF IQSec1, and that both IQSec1 and Arf5 activation are essential for adhesion disassembly. We further show that IQSec1 forms a complex with the lipid transfer protein ORP3, and that Ca2+ influx triggers PKC-dependent translocation of this complex to ER/plasma membrane contact sites adjacent to FAs. In addition to allosterically activating IQSec1, ORP3 also extracts PI4P from the PM, in exchange for phosphatidylcholine. ORP3-mediated lipid exchange is also important for FA turnover. Together, these findings identify a new pathway that links calcium influx to FA turnover during cell migration.

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.

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