Lipid traffic: floppy drives and a superhighway

KEY POINTS * Eukaryotic cells contain hundreds of different lipid species that are distributed unevenly between subcellular organelles and also between the two leaflets of the bilayer of

each organelle. Non-random lipid distributions are maintained despite extensive membrane trafficking between different organelles, and cannot be explained by local metabolism alone. * Lipids

in cells are subject to sorting, and this process probably involves the capacity of lipids to self-organize into phase-separated microdomains. However, a general consensus on the size,

shape and dynamics of such lipid microdomains is lacking at present. * Phospholipids show a fast lateral diffusion in a bilayer, but the rate of their spontaneous flip–flop between the

leaflets is slow. Cells contain flippases that facilitate the energetically unfavourable movement of the phospholipid head group through the hydrophobic membrane interior, and these

activities are increasingly being attributed to specific proteins. * Flippases have a key role in membrane stability, as well as in the mechanism by which cells avoid being killed by

macrophages. By expanding one membrane leaflet at the expense of the other, unidirectional flippases might participate in membrane folding and vesiculation. * The trafficking of particular

lipids between organelles is mediated by lipid-transfer proteins that shuttle across cytosolic gaps. For them to function efficiently, these proteins must target both donor and acceptor

membranes, and the proteins that have been identified as having such a dual-membrane-targeting ability are found at sites where the two membranes are in close proximity. * Flippases and

lipid-transfer proteins both move lipids over short distances (approximately 10 nm), whereas other mechanisms — such as vesicular trafficking and diffusion within individual pan-cellular

organelles (in particular, the endoplasmic reticulum) — can move lipids across the whole cell. ABSTRACT Understanding how membrane lipids achieve their non-random distribution in cells is a

key challenge in cell biology at present. In addition to being sorted into vesicles that can cross distances of up to one metre, there are other mechanisms that mediate the transport of

lipids within a range of a few nanometres. These include transbilayer flip–flop mechanisms and transfer across narrow gaps between the endoplasmic reticulum and other organelles, with the

endoplasmic reticulum functioning as a superhighway along which lipids can rapidly diffuse. Access through your institution Buy or subscribe This is a preview of subscription content, access

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DISTRIBUTION Article Open access 30 November 2023 STRUCTURAL AND FUNCTIONAL CONSEQUENCES OF REVERSIBLE LIPID ASYMMETRY IN LIVING MEMBRANES Article 16 November 2020 REGULATION OF MEMBRANE

PROTEIN STRUCTURE AND FUNCTION BY THEIR LIPID NANO-ENVIRONMENT Article 02 September 2022 REFERENCES * Schekman, R. Merging cultures in the study of membrane traffic. _Nature Cell Biol._ 6,

483–486 (2004). CAS  PubMed  Google Scholar  * Murase, K. et al. Ultrafine membrane compartments for molecular diffusion as revealed by single molecule techniques. _Biophys. J._ 86,

4075–4093 (2004). CAS  PubMed  PubMed Central  Google Scholar  * Irvine, R. Inositol lipids: to PHix or not to PHix? _Curr. Biol._ 14, R308–R310 (2004). CAS  PubMed  Google Scholar  *

Kornberg, R. D. & McConnell, H. M. Inside–outside transitions of phospholipids in vesicle membranes. _Biochemistry_ 10, 1111–1120 (1971). CAS  PubMed  Google Scholar  * Bai, J. &

Pagano, R. E. Measurement of spontaneous transfer and transbilayer movement of BODIPY-labeled lipids in lipid vesicles. _Biochemistry_ 36, 8840–8848 (1997). CAS  PubMed  Google Scholar  *

Bretscher, M. S. Membrane structure: some general principles. _Science_ 181, 622–629 (1973). CAS  PubMed  Google Scholar  * Bishop, W. R. & Bell, R. M. Assembly of the endoplasmic

reticulum phospholipid bilayer: the phosphatidylcholine transporter. _Cell_ 42, 51–60 (1985). USING A SHORT-CHAIN LIPID ANALOGUE, THE AUTHORS DISCOVER A FAST TRANSPORT SYSTEM FOR PC IN RAT

LIVER MICROSOMES THAT IS SATURABLE AND SENSITIVE TO PROTEIN-MODIFYING AGENTS. CAS  PubMed  Google Scholar  * Buton, X., Morrot, G., Fellmann, P. & Seigneuret, M. Ultrafast

glycerophospholipid-selective transbilayer motion mediated by a protein in the endoplasmic reticulum membrane. _J. Biol. Chem._ 271, 6651–6657 (1996). CAS  PubMed  Google Scholar  *

Seigneuret, M. & Devaux, P. F. ATP-dependent asymmetric distribution of spin-labeled phospholipids in the erythrocyte membrane: relation to shape changes. _Proc. Natl Acad. Sci. USA_ 81,

3751–3755 (1984). CAS  PubMed  PubMed Central  Google Scholar  * Daleke, D. L. Regulation of transbilayer plasma membrane phospholipid asymmetry. _J. Lipid Res._ 44, 233–242 (2003). CAS 

PubMed  Google Scholar  * Fadok, V. A. et al. A receptor for phosphatidylserine-specific clearance of apoptotic cells. _Nature_ 405, 85–90 (2000). Article  CAS  PubMed  Google Scholar  *

McLean, L. R. & Phillips, M. C. Kinetics of phosphatidylcholine and lysophosphatidylcholine exchange between unilamellar vesicles. _Biochemistry_ 23, 4624–4630 (1984). CAS  PubMed 

Google Scholar  * Voelker, D. R. New perspectives on the regulation of intermembrane glycerophospholipid traffic. _J. Lipid Res._ 44, 441–449 (2003). CAS  PubMed  Google Scholar  * Vance, J.

E. Phospholipid synthesis in a membrane fraction associated with mitochondria. _J. Biol. Chem._ 265, 7248–7256 (1990). CAS  PubMed  Google Scholar  * Kaplan, M. R. & Simoni, R. D.

Intracellular transport of phosphatidylcholine to the plasma membrane. _J. Cell Biol._ 101, 441–445 (1985). CAS  PubMed  Google Scholar  * Gnamusch, E., Kalaus, C., Hrastnik, C., Paltauf, F.

& Daum, G. Transport of phospholipids between subcellular membranes of wild-type yeast cells and of the phosphatidylinositol transfer protein-deficient strain _Saccharomyces cerevisiae_

sec14. _Biochim. Biophys. Acta_ 1111, 120–126 (1992). CAS  PubMed  Google Scholar  * Sleight, R. G. & Pagano, R. E. Rapid appearance of newly synthesized phosphatidylethanolamine at the

plasma membrane. _J. Biol. Chem._ 258, 9050–9058 (1983). CAS  PubMed  Google Scholar  * Funato, K. & Riezman, H. Vesicular and nonvesicular transport of ceramide from ER to the Golgi

apparatus in yeast. _J. Cell Biol._ 155, 949–959 (2001). CAS  PubMed  PubMed Central  Google Scholar  * Hanada, K. et al. Molecular machinery for non-vesicular trafficking of ceramide.

_Nature_ 426, 803–809 (2003). IDENTIFIES A CERAMIDE TRANSPORTER IN MAMMALIAN CELLS THAT CONTAINS A START DOMAIN THAT IS SPECIFIC FOR CERAMIDE, AS WELL AS TARGETING DOMAINS FOR THE ER AND

GOLGI. CAS  PubMed  Google Scholar  * Bankaitis, V. A., Aitken, J. R., Cleves, A. E. & Dowhan, W. An essential role for a phospholipid transfer protein in yeast Golgi function. _Nature_

347, 561–562 (1990). CAS  PubMed  Google Scholar  * Whatmore, J., Wiedemann, C., Somerharju, P., Swigart, P. & Cockcroft, S. Resynthesis of phosphatidylinositol in permeabilized

neutrophils following phospholipase Cβ activation: transport of the intermediate, phosphatidic acid, from the plasma membrane to the endoplasmic reticulum for phosphatidylinositol

resynthesis is not dependent on soluble lipid carriers or vesicular transport. _Biochem. J._ 341, 435–444 (1999). CAS  PubMed  PubMed Central  Google Scholar  * Puri, V. et al. Sphingolipid

storage induces accumulation of intracellular cholesterol by stimulating SREBP-1 cleavage. _J. Biol. Chem._ 278, 20961–20970 (2003). CAS  PubMed  Google Scholar  * McConnell, H. M. &

Vrljic, M. Liquid–liquid immiscibility in membranes. _Annu. Rev. Biophys. Biomol. Struct._ 32, 469–492 (2003). CAS  PubMed  Google Scholar  * Malathi, K. et al. Mutagenesis of the putative

sterol-sensing domain of yeast Niemann Pick C-related protein reveals a primordial role in subcellular sphingolipid distribution. _J. Cell Biol._ 164, 547–556 (2004). CAS  PubMed  PubMed

Central  Google Scholar  * Burger, K. N., van der Bijl, P. & van Meer, G. Topology of sphingolipid galactosyltransferases in ER and Golgi: transbilayer movement of monohexosyl

sphingolipids is required for higher glycosphingolipid biosynthesis. _J. Cell Biol._ 133, 15–28 (1996). CAS  PubMed  Google Scholar  * Huitema, K., Van Den Dikkenberg, J., Brouwers, J. F.

& Holthuis, J. C. Identification of a family of animal sphingomyelin synthases. _EMBO J._ 23, 33–44 (2004). CAS  PubMed  Google Scholar  * Buton, X. et al. Transbilayer movement of

monohexosylsphingolipids in endoplasmic reticulum and Golgi membranes. _Biochemistry_ 41, 13106–13115 (2002). CAS  PubMed  Google Scholar  * Brugger, B. et al. Evidence for segregation of

sphingomyelin and cholesterol during formation of COPI-coated vesicles. _J. Cell Biol._ 151, 507–518 (2000). CAS  PubMed  PubMed Central  Google Scholar  * Baumgart, T., Hess, S. T. &

Webb, W. W. Imaging coexisting fluid domains in biomembrane models coupling curvature and line tension. _Nature_ 425, 821–824 (2003). THIS HIGH-RESOLUTION FLUORESCENCE-IMAGING STUDY ON MODEL

MEMBRANES SHOWS HOW LIPID IMMISCIBILITY AND DOMAIN FORMATION ARE COUPLED TO MEMBRANE-BUDDING AND -FISSION EVENTS. CAS  PubMed  Google Scholar  * Munro, S. Lipid rafts: elusive or illusive?

_Cell_ 115, 377–388 (2003). A CRITICAL ASSESSMENT OF THE EXPERIMENTAL EVIDENCE FOR THE EXISTENCE OF LIPID MICRODOMAINS IN CELLULAR MEMBRANES. CAS  PubMed  Google Scholar  * Schneiter, R. et

al. Electrospray ionization tandem mass spectrometry (ESI–MS/MS) analysis of the lipid molecular species composition of yeast subcellular membranes reveals acyl chain-based

sorting/remodeling of distinct molecular species en route to the plasma membrane. _J. Cell Biol._ 146, 741–754 (1999). CAS  PubMed  PubMed Central  Google Scholar  * Grove, S. N., Bracker,

C. E. & Morré, D. J. Cytomembrane differentiation in the endoplasmic reticulum–Golgi apparatus–vesicle complex. _Science_ 161, 171–173 (1968). CAS  PubMed  Google Scholar  * Mitra, K.,

Ubarretxena-Belandia, I., Taguchi, T., Warren, G. & Engelman, D. M. Modulation of the bilayer thickness of exocytic pathway membranes by membrane proteins rather than cholesterol. _Proc.

Natl Acad. Sci. USA_ 101, 4083–4088 (2004). CAS  PubMed  PubMed Central  Google Scholar  * Bretscher, M. S. & Munro, S. Cholesterol and the Golgi apparatus. _Science_ 261, 1280–1281

(1993). CAS  PubMed  Google Scholar  * Munro, S. An investigation of the role of transmembrane domains in Golgi protein retention. _EMBO J._ 14, 4695–4704 (1995). CAS  PubMed  PubMed Central

  Google Scholar  * Cole, N. B., Ellenberg, J., Song, J., DiEuliis, D. & Lippincott-Schwartz, J. Retrograde transport of Golgi-localized proteins to the ER. _J. Cell Biol._ 140, 1–15

(1998). CAS  PubMed  PubMed Central  Google Scholar  * Folsch, H., Ohno, H., Bonifacino, J. S. & Mellman, I. A novel clathrin adaptor complex mediates basolateral targeting in polarized

epithelial cells. _Cell_ 99, 189–198 (1999). CAS  PubMed  Google Scholar  * Simons, K. & Ikonen, E. Functional rafts in cell membranes. _Nature_ 387, 569–572 (1997). CAS  PubMed  Google

Scholar  * Polishchuk, R., Di Pentima, A. & Lippincott-Schwartz, J. Delivery of raft-associated, GPI-anchored proteins to the apical surface of polarized MDCK cells by a transcytotic

pathway. _Nature Cell Biol._ 6, 297–307 (2004). THIS LIVE-CELL-IMAGING STUDY INDICATES THAT THE PRIMARY SITE FOR THE APICAL SORTING OF LIPID-MICRODOMAIN-ASSOCIATED GPI-ANCHORED PROTEINS IS

THE BASOLATERAL PLASMA MEMBRANE RATHER THAN THE _TRANS_ -GOLGI NETWORK. CAS  PubMed  Google Scholar  * Parton, R. G. Caveolae — from ultrastructure to molecular mechanisms. _Nature Rev. Mol.

Cell Biol._ 4, 162–167 (2003). CAS  Google Scholar  * Singh, R. D. et al. Selective caveolin-1-dependent endocytosis of glycosphingolipids. _Mol. Biol. Cell_ 14, 3254–3265 (2003). CAS 

PubMed  PubMed Central  Google Scholar  * Menon, A. K., Watkins, W. E. & Hrafnsdottir, S. Specific proteins are required to translocate phosphatidylcholine bidirectionally across the

endoplasmic reticulum. _Curr. Biol._ 10, 241–252 (2000). CAS  PubMed  Google Scholar  * Kol, M. A. et al. Phospholipid flop induced by transmembrane peptides in model membranes is modulated

by lipid composition. _Biochemistry_ 42, 231–327 (2003). CAS  PubMed  Google Scholar  * Helenius, J. et al. Translocation of lipid-linked oligosaccharides across the ER membrane requires

Rft1 protein. _Nature_ 415, 447–450 (2002). CAS  PubMed  Google Scholar  * Zhou, Q. et al. Molecular cloning of human plasma membrane phospholipid scramblase. A protein mediating

transbilayer movement of plasma membrane phospholipids. _J. Biol. Chem._ 272, 18240–18244 (1997). CAS  PubMed  Google Scholar  * Zhou, Q., Zhao, J., Wiedmer, T. & Sims, P. J. Normal

hemostasis but defective hematopoietic response to growth factors in mice deficient in phospholipid scramblase 1. _Blood_ 99, 4030–4038 (2002). CAS  PubMed  Google Scholar  * Hirsch, D.,

Stahl, A. & Lodish, H. F. A family of fatty acid transporters conserved from mycobacterium to man. _Proc. Natl Acad. Sci. USA_ 95, 8625–8629 (1998). CAS  PubMed  PubMed Central  Google

Scholar  * Pomorski, T., Holthuis, J. C., Herrmann, A. & van Meer, G. Tracking down lipid flippases and their biological functions. _J. Cell Sci._ 117, 805–813 (2004). CAS  PubMed 

Google Scholar  * Natarajan, P., Wang, J., Hua, Z. & Graham, T. R. Drs2p-coupled aminophospholipid translocase activity in yeast Golgi membranes and relationship to _in vivo_ function.

_Proc. Natl Acad. Sci. USA_ 101, 10614–10619 (2004). CAS  PubMed  PubMed Central  Google Scholar  * Pomorski, T. et al. Drs2p-related P-type ATPases Dnf1p and Dnf2p are required for

phospholipid translocation across the yeast plasma membrane and serve a role in endocytosis. _Mol. Biol. Cell_ 14, 1240–1254 (2003). PROVIDES EVIDENCE FOR A FUNCTIONAL LINK BETWEEN

P-TYPE-ATPASE-DEPENDENT LIPID TRANSPORT AND ENDOCYTIC-VESICLE FORMATION. CAS  PubMed  PubMed Central  Google Scholar  * Tang, X., Halleck, M. S., Schlegel, R. A. & Williamson, P. A

subfamily of P-type ATPases with aminophospholipid transporting activity. _Science_ 272, 1495–1497 (1996). USING PEPTIDE SEQUENCES FROM A PURIFIED, BOVINE CHROMAFFIN-GRANULE

AMINOPHOSPHOLIPID-TRANSLOCASE ACTIVITY, THE AUTHORS DISCOVER A NEW SUBFAMILY OF P-TYPE ATPASES THAT HAVE A CRUCIAL FUNCTION IN AMINOPHOSPHOLIPID TRANSPORT. CAS  PubMed  Google Scholar  *

Gomes, E., Jakobsen, M. K., Axelsen, K. B., Geisler, M. & Palmgren, M. G. Chilling tolerance in _Arabidopsis_ involves ALA1, a member of a new family of putative aminophospholipid

translocases. _Plant Cell_ 12, 2441–2454 (2000). CAS  PubMed  PubMed Central  Google Scholar  * Bull, L. N. et al. A gene encoding a P-type ATPase mutated in two forms of hereditary

cholestasis. _Nature Genet._ 18, 219–224 (1998). CAS  PubMed  Google Scholar  * Meguro, M. et al. A novel maternally expressed gene, ATP10C, encodes a putative aminophospholipid translocase

associated with Angelman syndrome. _Nature Genet._ 28, 19–20 (2001). CAS  PubMed  Google Scholar  * Chen, C. Y., Ingram, M. F., Rosal, P. H. & Graham, T. R. Role for Drs2p, a P-type

ATPase and potential aminophospholipid translocase, in yeast late Golgi function. _J. Cell Biol._ 147, 1223–1236 (1999). CAS  PubMed  PubMed Central  Google Scholar  * Hua, Z., Fatheddin, P.

& Graham, T. R. An essential subfamily of Drs2p-related P-type ATPases is required for protein trafficking between Golgi complex and endosomal/vacuolar system. _Mol. Biol. Cell_ 13,

3162–3177 (2002). CAS  PubMed  PubMed Central  Google Scholar  * Devaux, P. F. Is lipid translocation involved during endo- and exocytosis? _Biochimie_ 82, 497–509 (2000). INSIGHTFUL REVIEW

ON THE PHYSICAL CONSTRAINTS OF MEMBRANE FOLDING AND THE PUTATIVE ROLE OF LIPID TRANSLOCASES IN VESICLE FORMATION. CAS  PubMed  Google Scholar  * Muller, P., Pomorski, T. & Herrmann, A.

Incorporation of phospholipid analogues into the plasma membrane affects ATP-induced vesiculation of human erythrocyte ghosts. _Biochem. Biophys. Res. Commun._ 199, 881–887 (1994). CAS 

PubMed  Google Scholar  * Saito, K. et al. Cdc50p, a protein required for polarized growth, associates with the Drs2p P-type ATPase implicated in phospholipid translocation in _Saccharomyces

cerevisiae_. _Mol. Biol. Cell_ 15, 3418–3432 (2004). CAS  PubMed  PubMed Central  Google Scholar  * Weng, J. et al. Insights into the function of Rim protein in photoreceptors and etiology

of Stargardt's disease from the phenotype in _abcr_ knockout mice. _Cell_ 98, 13–23 (1999). CAS  PubMed  Google Scholar  * Smit, J. J. M. et al. Homozygous disruption of the murine

_mdr2_ P-glycoprotein gene leads to a complete absence of phospholipid from bile and to liver disease. _Cell_ 75, 451–462 (1993). CAS  PubMed  Google Scholar  * van Helvoort, A. et al. MDR1

P-glycoprotein is a lipid translocase of broad specificity, while MDR3 P-glycoprotein specifically translocates phosphatidylcholine. _Cell_ 87, 507–517 (1996). CAS  PubMed  Google Scholar  *

Decottignies, A. et al. ATPase and multidrug transport activities of the overexpressed yeast ABC protein Yor1p. _J. Biol. Chem._ 273, 12612–12622 (1998). CAS  PubMed  Google Scholar  *

Hamon, Y. et al. ABC1 promotes engulfment of apoptotic cells and transbilayer redistribution of phosphatidylserine. _Nature Cell Biol._ 2, 399–406 (2000). CAS  PubMed  Google Scholar  *

Berge, K. E. et al. Accumulation of dietary cholesterol in sitosterolemia caused by mutations in adjacent ABC transporters. _Science_ 290, 1771–1775 (2000). CAS  PubMed  Google Scholar  *

Hettema, E. H. et al. The ABC transporter proteins Pat1 and Pat2 are required for import of long-chain fatty acids into peroxisomes of _Saccharomyces cerevisiae_. _EMBO J._ 15, 3813–3822

(1996). CAS  PubMed  PubMed Central  Google Scholar  * Kihara, A. & Igarashi, Y. Identification and characterization of a _Saccharomyces cerevisiae_ gene, _RSB1_, involved in sphingoid

long-chain base release. _J. Biol. Chem._ 277, 30048–30054 (2002). CAS  PubMed  Google Scholar  * Wirtz, K. W. Phospholipid transfer proteins. _Annu. Rev. Biochem._ 60, 73–99 (1991). CAS 

PubMed  Google Scholar  * Schouten, A. et al. Structure of apo-phosphatidylinositol transfer protein α provides insight into membrane association. _EMBO J._ 21, 2117–2121 (2002). CAS  PubMed

  PubMed Central  Google Scholar  * Sha, B., Phillips, S. E., Bankaitis, V. A. & Luo, M. Crystal structure of the _Saccharomyces cerevisiae_ phosphatidylinositol-transfer protein.

_Nature_ 391, 506–510 (1998). CAS  PubMed  Google Scholar  * Tsujishita, Y. & Hurley, J. H. Structure and lipid transport mechanism of a StAR-related domain. _Nature Struct. Biol._ 7,

408–414 (2000). CAS  PubMed  Google Scholar  * Schrick, K., Nguyen, D., Karlowski, W. M. & Mayer, K. F. START lipid/sterol-binding domains are amplified in plants and are predominantly

associated with homeodomain transcription factors. _Genome Biol._ 5, R41 (2004). PubMed  PubMed Central  Google Scholar  * Debant, A. et al. The multidomain protein Trio binds the LAR

transmembrane tyrosine phosphatase, contains a protein kinase domain, and has separate rac-specific and rho-specific guanine nucleotide exchange factor domains. _Proc. Natl Acad. Sci. USA_

93, 5466–5471 (1996). CAS  PubMed  PubMed Central  Google Scholar  * Munro, S. Organelle identity and the targeting of peripheral membrane proteins. _Curr. Opin. Cell Biol._ 14, 506–514

(2002). CAS  PubMed  Google Scholar  * Staehelin, L. A. The plant ER: a dynamic organelle composed of a large number of discrete functional domains. _Plant J._ 11, 1151–1165 (1997). CAS 

PubMed  Google Scholar  * Pichler, H. et al. A subfraction of the yeast endoplasmic reticulum associates with the plasma membrane and has a high capacity to synthesize lipids. _Eur. J.

Biochem._ 268, 2351–2361 (2001). CAS  PubMed  Google Scholar  * Mogelsvang, S., Marsh, B. J., Ladinsky, M. S. & Howell, K. E. Predicting function from structure: 3D structure studies of

the mammalian Golgi complex. _Traffic_ 5, 338–345 (2004). CAS  PubMed  Google Scholar  * Haj, F. G., Verveer, P. J., Squire, A., Neel, B. G. & Bastiaens, P. I. Imaging sites of receptor

dephosphorylation by PTP1B on the surface of the endoplasmic reticulum. _Science_ 295, 1708–1711 (2002). CONFIRMS THE FUNCTIONAL IMPORTANCE OF ER–ENDOSOME CONTACTS IN MAMMALIAN CELLS, BY

SHOWING THAT ENDOCYTOSED EPIDERMAL GROWTH FACTOR RECEPTOR IS DEPHOSPHORYLATED BY A PHOSPHATASE THAT IS EMBEDDED IN THE ER. CAS  PubMed  Google Scholar  * Pan, X. et al. Nucleus–vacuole

junctions in _Saccharomyces cerevisiae_ are formed through the direct interaction of Vac8p with Nvj1p. _Mol. Biol. Cell_ 11, 2445–2457 (2000). CAS  PubMed  PubMed Central  Google Scholar  *

Sinai, A. P. & Joiner, K. A. The _Toxoplasma gondii_ protein ROP2 mediates host organelle association with the parasitophorous vacuole membrane. _J. Cell Biol._ 154, 95–108 (2001). CAS 

PubMed  PubMed Central  Google Scholar  * Achleitner, G. et al. Association between the endoplasmic reticulum and mitochondria of yeast facilitates interorganelle transport of phospholipids

through membrane contact. _Eur. J. Biochem._ 264, 545–553 (1999). CAS  PubMed  Google Scholar  * Xu, C., Fan, J., Riekhof, W., Froehlich, J. E. & Benning, C. A permease-like protein

involved in ER to thylakoid lipid transfer in _Arabidopsis_. _EMBO J._ 22, 2370–2379 (2003). CAS  PubMed  PubMed Central  Google Scholar  * Milla, P. et al. Yeast oxidosqualene cyclase

(Erg7p) is a major component of lipid particles. _J. Biol. Chem._ 277, 2406–2412 (2002). CAS  PubMed  Google Scholar  * Underwood, K. W., Jacobs, N. L., Howley, A. & Liscum, L. Evidence

for a cholesterol transport pathway from lysosomes to endoplasmic reticulum that is independent of the plasma membrane. _J. Biol. Chem._ 273, 4266–4274 (1998). CAS  PubMed  Google Scholar  *

Coppens, I., Sinai, A. P. & Joiner, K. A. _Toxoplasma gondii_ exploits host low-density lipoprotein receptor-mediated endocytosis for cholesterol acquisition. _J. Cell Biol._ 149,

167–180 (2000). CAS  PubMed  PubMed Central  Google Scholar  * Shiao, Y. J., Balcerzak, B. & Vance, J. E. A mitochondrial membrane protein is required for translocation of

phosphatidylserine from mitochondria-associated membranes to mitochondria. _Biochem. J._ 331, 217–223 (1998). CAS  PubMed  PubMed Central  Google Scholar  * Severs, N. J., Jordan, E. G.

& Williamson, D. H. Nuclear pore absence from areas of close association between nucleus and vacuole in synchronous yeast cultures. _J. Ultrastruct. Res._ 54, 374–387 (1976). CAS  PubMed

  Google Scholar  * Rizzuto, R., Duchen, M. R. & Pozzan, T. Flirting in little space: the ER/mitochondria Ca2+ liaison. _Sci. STKE_ 2004, re1 (2004). PubMed  Google Scholar  * Loewen, C.

J., Roy, A. & Levine, T. P. A conserved ER targeting motif in three families of lipid binding proteins and in Opi1p binds VAP. _EMBO J._ 22, 2025–2035 (2003). IDENTIFIES A CONSERVED

INTERACTION BETWEEN VARIOUS LTPS AND THE ER, AND SHOWS THAT THIS TARGETING CAN BE INTEGRATED WITH PH-DOMAIN INTERACTIONS TO TARGET MCSS. CAS  PubMed  PubMed Central  Google Scholar  *

Vihtelic, T. S., Goebl, M., Milligan, S., O'Tousa, J. E. & Hyde, D. R. Localization of _Drosophila_ retinal degeneration B, a membrane-associated phosphatidylinositol transfer

protein. _J. Cell Biol._ 122, 1013–1022 (1993). CAS  PubMed  Google Scholar  * Milligan, S. C., Alb, J. G. Jr, Elagina, R. B., Bankaitis, V. A. & Hyde, D. R. The phosphatidylinositol

transfer protein domain of _Drosophila_ retinal degeneration B protein is essential for photoreceptor cell survival and recovery from light stimulation. _J. Cell Biol._ 139, 351–363 (1997).

CAS  PubMed  PubMed Central  Google Scholar  * Wu, W. I. & Voelker, D. R. Reconstitution of phosphatidylserine transport from chemically defined donor membranes to phosphatidylserine

decarboxylase 2 implicates specific lipid domains in the process. _J. Biol. Chem._ 279, 6635–6642 (2004). DISCUSSES A FUNCTIONAL ANALYSIS OF GENE PRODUCTS THAT WERE PREVIOUSLY IDENTIFIED TO

HAVE A ROLE IN THE NON-VESICULAR TRANSPORT OF PHOSPHATIDYLSERINE, AND DESCRIBES THE PRECISE BIOCHEMICAL REQUIREMENTS FOR LIPID EXTRACTION FROM DONOR MEMBRANES. CAS  PubMed  Google Scholar  *

Levine, T. P. & Munro, S. Targeting of Golgi-specific pleckstrin homology domains involves both PtdIns 4-kinase-dependent and-independent components. _Curr. Biol._ 12, 695–704 (2002).

CAS  PubMed  Google Scholar  * Novikoff, A. B. GERL, its form and function in neurons of rat spinal ganglia. _Biol. Bull._ 127, 358 (1964). Google Scholar  * Ridgway, N. D., Dawson, P. A.,

Ho, Y. K., Brown, M. S. & Goldstein, J. L. Translocation of oxysterol binding protein to Golgi apparatus triggered by ligand binding. _J. Cell Biol._ 116, 307–319 (1992). CAS  PubMed 

Google Scholar  * Alpy, F. et al. The steroidogenic acute regulatory protein homolog MLN64, a late endosomal cholesterol-binding protein. _J. Biol. Chem._ 276, 4261–4269 (2001). CAS  PubMed

  Google Scholar  * Cunningham, E. et al. The yeast and mammalian isoforms of phosphatidylinositol transfer protein can all restore phospholipase C-mediated inositol lipid signaling in

cytosol-depleted RBL-2H3 and HL-60 cells. _Proc. Natl Acad. Sci. USA_ 93, 6589–6593 (1996). CAS  PubMed  PubMed Central  Google Scholar  * Fleischer, B., Zambrano, F. & Fleischer, S.

Biochemical characterization of the Golgi complex of mammalian cells. _J. Supramol. Struct._ 2, 737–750 (1974). CAS  PubMed  Google Scholar  * Keenan, T. W. & Morre, D. J. Phospholipid

class and fatty acid composition of Golgi apparatus isolated from rat liver and comparison with other cell fractions. _Biochemistry_ 9, 19–25 (1970). CAS  PubMed  Google Scholar  *

Zachowski, A. Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement. _Biochem. J._ 294, 1–14 (1993). CAS  PubMed  PubMed Central  Google Scholar  * Leventis, R.

& Silvius, J. R. Use of cyclodextrins to monitor transbilayer movement and differential lipid affinities of cholesterol. _Biophys. J._ 81, 2257–2267 (2001). CAS  PubMed  PubMed Central 

Google Scholar  * Holthuis, J. C., van Meer, G. & Huitema, K. Lipid microdomains, lipid translocation and the organization of intracellular membrane transport. _Mol. Membr. Biol._ 20,

231–241 (2003). CAS  PubMed  Google Scholar  * Levine, T. P. Short-range intracellular traffic of small molecules via endoplasmic reticulum junctions. _Trends Cell Biol._ 9, 483–490 (2004).

Google Scholar  Download references ACKNOWLEDGEMENTS We apologize for the omission of many significant papers that could not be cited or discussed due to space limitations. Work in the

authors' laboratories is funded by grants from the Utrecht University High Potential Programme and the Netherlands Organization for Scientific Research (J.C.M.H.), and from The Wellcome

Trust, the Biotechnology and Biological Sciences Research Council, and Fight For Sight (T.P.L.). AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Membrane Enzymology, Institute

of Biomembranes, Utrecht University, Padualaan 8, Utrecht, 3584 CH, The Netherlands Joost C. M. Holthuis * Department of Cell Biology, Institute of Ophthalmology, 11–43 Bath Street, London,

EC1V 9EL, UK Tim P. Levine Authors * Joost C. M. Holthuis View author publications You can also search for this author inPubMed Google Scholar * Tim P. Levine View author publications You

can also search for this author inPubMed Google Scholar ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. SUPPLEMENTARY INFORMATION SUPPLEMENTARY

INFORMATION S1 (PDF 29 KB) SUPPLEMENTARY INFORMATION S2 (PDF 30 KB) RELATED LINKS RELATED LINKS DATABASES FLYBASE Rdgbα INTERPRO PH domain StART domain SACCHAROMYCES GENOME DATABASE Osh1

Osh2 Osh3 Psd2 Rsb1 Rft1 Sec14 Sfh4 SWISS-PROT ABCA1 ABCA4 ABCB1 ABCB4 ABCD1 ABCG5 ABCG8 CERT MLN64 ORP5 ORP8 OSBP PLSCR1 VAP GLOSSARY * WOBBLE Movement in which the lipid molecule partially

dips into the opposite leaflet of the bilayer and then moves back to its original position without changing its longitudinal orientation. * PHOSPHOINOSITIDE A phosphorylated derivative of

the glycerolipid phosphatidylinositol. As three positions of the inositol ring can be phosphorylated independently of each other, there are seven possible phosphoinositides. * BIOGENIC

MEMBRANE A membrane that can synthesize lipids. Biogenenic membranes include the plasma membrane in Gram-positive bacteria, the inner membrane in Gram-negative bacteria and the endoplasmic

reticulum in eukaryotes. * FLIPPASE A general term that refers to a protein, or protein complex, that facilitates the energetically unfavourable movement of the polar head group of a

phospholipid or glycosphingolipid through the hydrophobic interior of a membrane. * TRANSLOCASE A lipid translocase is a flippase that uses ATP hydrolysis to catalyse the unidirectional

movement of a lipid from one membrane leaflet to the other. Translocases help to create asymmetric lipid distributions across the bilayer. A well-known example is the aminophopsholipid

translocase that is responsible for the selective sequestration of phosphatidylserine and phosphatidylethanolamine in the cytosolic leaflet of the plasma membrane. * EXOPLASMIC LEAFLET The

non-cytosolic leaflet of a membrane, which faces the extracellular space or the lumen of an organelle. * SCRAMBLASE An energy-independent, bidirectional lipid flippase that, when activated

by a transient rise in intracellular Ca2+ levels, disrupts lipid asymmetry by facilitating a rapid equilibration of lipids between the two membrane leaflets. * EXOCYTIC PATHWAY Newly

synthesized proteins that are destined for the cell surface are first imported by the endoplasmic reticulum, then move through the Golgi complex and, finally, are packaged into secretory

vesicles that fuse with the plasma membrane. * _TRANS_-GOLGI The Golgi apparatus is composed of a stack of flattened cisternae (bags), which is asymmetric. Post-endoplasmic-reticulum

carriers fuse together to make the _cis_ side of the Golgi, whereas the _trans_ side is where post-Golgi carriers form. * ANTEROGRADE/RETROGRADE Terms that signify the direction in which

vesicles move. Cargo that is destined for the cell surface moves in the anterograde direction, and movement in the opposite direction, namely from the cell surface toward the endoplasmic

reticulum, is retrograde. * COPI-COATED VESICLES Transport vesicles that bud from the Golgi due to the assembly of a cytosolic coat protein known as coatomer protein (COP)I. * LIPID

MICRODOMAINS Lateral lipid assemblies that form spontaneously in the bilayer due to a differential miscibility of membrane lipids. Microdomains are typically enriched in sphingolipids and

sterols, and have been postulated to acquire specific functions by concentrating or excluding specific membrane proteins. Conversely, membrane proteins might affect microdomain size,

composition and lifespan. * APICAL MEMBRANE The region of the plasma membrane of an epithelial cell that faces the lumen. The region that is connected to the underlying tissue is known as

the basolateral membrane. * GPI-ANCHORED PROTEINS Proteins that are primarily found at the cell surface and that are attached to the bilayer by means of a lipid anchor, which is composed of

glycosylphosphatidylinositol (GPI). * P-TYPE ATPASES A ubiquitous family of polytopic membrane proteins that use the energy of ATP to transport ions across cellular membranes against a

concentration gradient. A distinctive biochemical feature of these pumps is an acid-stable phosphorylated aspartate residue that forms during the pumping cycle, and the phosphorylated (P)

intermediate gives the family its name. * FAMILIAL INTRAHEPATIC CHOLESTASIS A rare inherited condition in children, in which patients are unable to secrete bile from the liver, which often

progresses to an irreversible scarring of the liver (cirrhosis) within the first decade of life. * ANGELMAN SYNDROME A neurological disorder, also named 'happy puppet' syndrome, in

which severe learning difficulties are associated with a characteristic facial appearance and behaviour. * OUTER-SEGMENT DISC MEMBRANE The outer segment of rod cells contains a stack of

discs, which are each formed by a closed membrane in which the photoreceptor rhodopsin is embedded. * APOLIPOPROTEINS Proteins that form scaffolds for extracellular lipoprotein particles

that carry lipids (triglycerides and cholesterol esters) between the liver and peripheral tissues. * TANGIER DISEASE A genetic disorder that is characterized by a defect in the efflux of

cholesterol and its associated esters to high-density lipoproteins. The disease was first identified in a five-year-old inhabitant of the island of Tangier, located off the coast of

Virginia, USA. * ADRENOLEUKODYSTROPHY An inherited metabolic disorder in which the myelin sheath on nerve fibres is lost and the adrenal gland degenerates, which leads to progressive

neurological disability and death. People with adrenoleukodystrophy accumulate high levels of very-long-chain fatty acids in their brain and adrenal cortex, because the fatty acids are not

broken down in a normal manner. * PERIPHERAL MEMBRANE PROTEINS Proteins that have an affinity for a membrane because they bind to a membrane receptor (either another membrane protein or a

lipid head group). They do not integrate into the hydrophobic core of the bilayer. * PARASITOPHOROUS VACUOLE A membrane-bound organelle that contains an intracellular parasite, such as

_Toxoplasma gondii_. Although the membrane that surrounds this organelle is derived from the host, it is modified by the parasite to facilitate its survival and growth. * INTEGRAL MEMBRANE

PROTEIN A protein with a moiety (either a covalently linked lipid or a transmembrane domain) that is integrated into the hydrophobic core of the bilayer. * AVIDITY The overall measure of

binding between a multivalent ligand and its receptors. It was originally defined for antibodies, for which avidity refers to the overall strength of binding between multivalent antigens and

antibodies. * GOLGI–ER–LYSOSOME (GERL). This term, which has fallen into disuse, was used by Alex Novikoff to describe what is, at present, called the _trans_-endoplasmic reticulum (ER) —

that is, flattened ER cisternae that are intercalated between cisternae of the _trans_-Golgi. Claims of direct membrane continuity between GERL and adjacent lysosomes have not been

substantiated. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Holthuis, J., Levine, T. Lipid traffic: floppy drives and a superhighway. _Nat Rev Mol

Cell Biol_ 6, 209–220 (2005). https://doi.org/10.1038/nrm1591 Download citation * Issue Date: 01 March 2005 * DOI: https://doi.org/10.1038/nrm1591 SHARE THIS ARTICLE Anyone you share the

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