Vesicular and nonvesicular transport of ceramide from ER to the Golgi apparatus in yeast.
Transport and sorting of lipids must occur with specific mechanisms because the membranes of intracellular organelles differ in lipid composition even though most lipid biosynthesis begins in the ER. In yeast, ceramide is synthesized in the ER and transferred to the Golgi apparatus where inositolphosphorylceramide (IPC) is formed. These two facts imply that ceramide can be transported to the Golgi independent of vesicular traffic because IPC synthesis still continues when vesicular transport is blocked in sec mutants. Nonvesicular IPC synthesis in intact cells is not affected by ATP depletion. Using an in vitro assay that reconstitutes the nonvesicular pathway for transport of ceramide, we found that transport is temperature and cytosol dependent but energy independent. Preincubation of ER and Golgi fractions together at 4 degrees C, where ceramide transport does not occur, rendered the transport reaction membrane concentration independent, providing biochemical evidence that ER-Golgi membrane contacts stimulate ceramide transport. A cytosolic protease-sensitive factor is required after establishment of ER-Golgi contacts.
Funato
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Biozentrum of the University of Basel, CH-4056 Basel, Switzerland.
Riezman
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D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D022181:COP-Coated Vesicles; D002352:Carrier Proteins / Q000235:genetics; D002474:Cell-Free System; D002518:Ceramides / Q000096:biosynthesis / Q000378:metabolism*; D022162:Cytoplasmic Vesicles / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics; D020690:GTPase-Activating Proteins; D006028:Glycosphingolipids / Q000096:biosynthesis / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D008562:Membrane Glycoproteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D009154:Mutation / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013107:Sphingolipids / Q000096:biosynthesis; D033921:Vesicular Transport Proteins; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; D002518:Ceramides; D005656:Fungal Proteins; D020690:GTPase-Activating Proteins; D006028:Glycosphingolipids; D020662:Guanine Nucleotide Exchange Factors; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C071239:SEC12 protein, S cerevisiae; C096367:SEC16 protein, S cerevisiae; C075137:SEC17 protein, S cerevisiae; C079037:SEC23 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013107:Sphingolipids; D033921:Vesicular Transport Proteins; C025524:inositolphosphoceramides; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C064404:SEC18 protein, S cerevisiae