Lipid rafts function in biosynthetic delivery of proteins to the cell surface in yeast

Bagnat, Michel

doi:10.1073/pnas.060034697

Cited by 303 publications

(432 citation statements)

References 22 publications

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“…At the cell surface, Pma1 becomes stabilized by a poorly characterized mechanism and occupies detergent-resistant domains that are distinct from those occupied by the arginine/H þ symporter Can1 [9,10]. From the plasma membrane, Pma1 is finally recycled and turned-over by endocytic delivery to the vacuole.…”

Section: Biogenesis and Transport Of The Proton Pumping H D -Atpasementioning

confidence: 99%

Lipid-dependent surface transport of the proton pumping ATPase: A model to study plasma membrane biogenesis in yeast

Toulmay

Schneiter

2007

Biochimie

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The proton pumping H þ -ATPase, Pma1, is one of the most abundant integral membrane proteins of the yeast plasma membrane. Pma1 activity controls the intracellular pH and maintains the electrochemical gradient across the plasma membrane, two essential cellular functions. The maintenance of the proton gradient, on the other hand, also requires a specialized lipid composition of this membrane. The plasma membrane of eukaryotic cells is typically rich in sphingolipids and sterols. These two lipids condense to form less fluid membrane microdomains or lipid rafts. The yeast sphingolipid is peculiar in that it invariably contains a saturated very long-chain fatty acid with 26 carbon atoms. During cell growth and plasma membrane expansion, both C26-containing sphingolipids and Pma1 are first synthesized in the endoplasmatic reticulum from where they are transported by the secretory pathway to the cell surface. Remarkably, shortening the C26 fatty acid to a C22 fatty acid by mutations in the fatty acid elongation complex impairs raft association of newly synthesized Pma1 and induces rapid degradation of the ATPase by rerouting the enzyme from the plasma membrane to the vacuole, the fungal equivalent of the lysosome. Here, we review the role of lipids in mediating raft association and stable surface transport of the newly synthesized ATPase, and discuss a model, in which the newly synthesized ATPase assembles into a membrane environment that is enriched in C26-containing lipids already in the endoplasmatic reticulum. The resulting proteinelipid complex is then transported and sorted as an entity to the plasma membrane. Failure to successfully assemble this lipideprotein complex results in mistargeting of the protein to the vacuole.

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Section: Biogenesis and Transport Of The Proton Pumping H D -Atpasementioning

confidence: 99%

Lipid-dependent surface transport of the proton pumping ATPase: A model to study plasma membrane biogenesis in yeast

Toulmay

Schneiter

2007

Biochimie

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“…Flotation gradients were essentially performed as described in Bagnat et al (2000). Briefly, cells were grown to logarithmic phase in YPD.…”

Section: Flotation Gradientsmentioning

confidence: 99%

The Deubiquitinating Enzyme Ubp1 Affects Sorting of the ATP-binding Cassette-Transporter Ste6 in the Endocytic Pathway

Schmitz

Kinner

Kölling

2005

MBoC

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Deubiquitinating enzymes (Dubs) are potential regulators of ubiquitination-dependent processes. Here, we focus on a member of the yeast ubiquitin-specific processing protease (Ubp) family, the Ubp1 protein. We could show that Ubp1 exists in two forms: a longer membrane-anchored form (mUbp1) and a shorter soluble form (sUbp1) that seem to be independently expressed from the same gene. The membrane-associated mUbp1 variant could be localized to the endoplasmic reticulum (ER) membrane by sucrose density gradient centrifugation and by immunofluorescence microscopy. Overexpression of the soluble Ubp1 variant stabilizes the ATP-binding cassette-transporter Ste6, which is transported to the lysosome-like vacuole for degradation, and whose transport is regulated by ubiquitination. Ste6 stabilization was not the result of a general increase in deubiquitination activity, because overexpression of Ubp1 had no effect on the degradation of the ER-associated degradation substrate carboxypeptidase Y* and most importantly on Ste6 ubiquitination itself. Also, overexpression of another yeast Dub, Ubp3, had no effect on Ste6 turnover. This suggests that the Ubp1 target is a component of the protein transport machinery. On Ubp1 overexpression, Ste6 accumulates at the cell surface, which is consistent with a role of Ubp1 at the internalization step of endocytosis or with enhanced recycling to the cell surface from an internal compartment. INTRODUCTIONMany cellular proteins are modified by the attachment of the 76-amino acid polypeptide ubiquitin (Hochstrasser, 1996;Hershko and Ciechanover, 1998). The main role of ubiquitination is to target proteins for degradation either directly by acting as a degradation signal that is recognized by the 26S proteasome or indirectly by sorting membrane proteins into the lysosomal/vacuolar degradation pathway (Hicke, 1999). Ubiquitination of substrate proteins, which occurs by a cascade of enzymatic reactions, is reversible. Ubiquitin can again be removed from proteins by deubiquitinating enzymes (Dubs). A large number of Dubs have been identified in various organisms that are either cysteine proteases or metalloproteases (Verma et al., 2002; Yao and Cohen, 2002). The more classical cysteine proteases can again be divided into two groups: the ubiquitin C-terminal hydrolases (Uchs) that preferentially cleave ubiquitin from peptides and small adducts (e.g., Yuh1 in yeast) and the extremely divergent family of ubiquitin-specific processing proteases (Ubps) that cleave ubiquitin from protein substrates (Hochstrasser, 1996). Of the 17 cysteine-protease-type Dubs in yeast 16 belong to the Ubp class.The degree of ubiquitination seems to be mainly regulated at the level of ubiquitin attachment. However, evidence is accumulating that deubiquitination also can be important for the regulation of ubiquitination levels. Evidence has been presented that the deubiquitinating enzyme Fat facets (Faf), which is involved in eye development in Drosophila, acts as a substrate-specific regulator of ubiquitination of the...

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“…brane (Bagnat et al, 2000;Umebayashi and Nakano, 2003). Proper transcriptional regulation of ERG genes has also been shown to be necessary for vacuole assembly (Hongay et al, 2002).…”

Section: Ergosterol Requirement For Vacuole Biogenesismentioning

confidence: 99%

Enhanced Membrane Fusion in Sterol-enriched Vacuoles Bypasses the Vrp1p Requirement

Tedrick

Trischuk

Lehner

et al. 2004

MBoC

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Organization of lipids into membrane microdomains is a vital mechanism of protein processing. Here we show that overexpression of ERG6, a gene involved in ergosterol synthesis, elevates sterol levels 1.5-fold on the vacuole membrane and enhances their homotypic fusion. The mechanism of sterol-enhanced fusion is not via more efficient sorting, but instead promotes increased kinetics of fusion subreactions. We initially isolated ERG6 as a suppressor of a vrp1⌬ growth defect selective for vacuole function. VRP1 encodes verprolin, an actin-binding protein that colocalizes to vacuoles. The vrp1⌬ mutant has fragmented vacuoles in vivo and isolated vacuoles do not fuse in vitro, indicative of a Vrp1p requirement for membrane fusion. ERG6 overexpression rescues vrp1⌬ vacuole fusion in a cytosol-dependent manner. Cytosol prepared from the vrp1⌬ strain remains active; therefore, cytosol is not resupplying Vrp1p. Las17p (Vrp1p functional partner) antibodies, which inhibit wild-type vacuole fusion, do not inhibit the fusion of vacuoles from the vrp1⌬-ERG6 overexpression strain. Vacuole-associated actin turnover is decreased in the vrp1⌬ strain, but recovered by ERG6 overexpression linking sterol enrichment to actin remodeling. Therefore, the Vrp1p/Las17p requirement for membrane fusion is bypassed by increased sterols, which promotes actin remodeling as part the membrane fusion mechanism.

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Lipid rafts function in biosynthetic delivery of proteins to the cell surface in yeast

Cited by 303 publications

References 22 publications

Lipid-dependent surface transport of the proton pumping ATPase: A model to study plasma membrane biogenesis in yeast

Lipid-dependent surface transport of the proton pumping ATPase: A model to study plasma membrane biogenesis in yeast

The Deubiquitinating Enzyme Ubp1 Affects Sorting of the ATP-binding Cassette-Transporter Ste6 in the Endocytic Pathway

Enhanced Membrane Fusion in Sterol-enriched Vacuoles Bypasses the Vrp1p Requirement

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