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Dynamic ergosterol- and ceramide-rich domains in the peroxisomal membrane serve as an organizing platform for peroxisome fusion.

Boukh-Viner T, Guo T, Alexandrian A, Cerracchio A, Gregg C, Haile S, Kyskan R, Milijevic S, Oren D, Solomon J, Wong V, Nicaud JM, Rachubinski RA, English AM, Titorenko VI - J. Cell Biol. (2005)

Bottom Line: We describe unusual ergosterol- and ceramide-rich (ECR) domains in the membrane of yeast peroxisomes.Several key features of these detergent-resistant domains, including the nature of their sphingolipid constituent and its unusual distribution across the membrane bilayer, clearly distinguish them from well characterized detergent-insoluble lipid rafts in the plasma membrane.A distinct set of peroxisomal proteins, including two ATPases, Pex1p and Pex6p, as well as phosphoinositide- and GTP-binding proteins, transiently associates with the cytosolic face of ECR domains.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Concordia University, Montreal, Quebec H4B 1R6, Canada.

ABSTRACT
We describe unusual ergosterol- and ceramide-rich (ECR) domains in the membrane of yeast peroxisomes. Several key features of these detergent-resistant domains, including the nature of their sphingolipid constituent and its unusual distribution across the membrane bilayer, clearly distinguish them from well characterized detergent-insoluble lipid rafts in the plasma membrane. A distinct set of peroxisomal proteins, including two ATPases, Pex1p and Pex6p, as well as phosphoinositide- and GTP-binding proteins, transiently associates with the cytosolic face of ECR domains. All of these proteins are essential for the fusion of the immature peroxisomal vesicles P1 and P2, the earliest intermediates in a multistep pathway leading to the formation of mature, metabolically active peroxisomes. Peroxisome fusion depends on the lateral movement of Pex1p, Pex6p, and phosphatidylinositol-4,5-bisphosphate-binding proteins from ECR domains to a detergent-soluble portion of the membrane, followed by their release to the cytosol. Our data suggest a model for the multistep reorganization of the multicomponent peroxisome fusion machinery that transiently associates with ECR domains.

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A model for the multistep remodeling of the peroxisome fusion machinery. The multicomponent peroxisome fusion machinery, which only transiently resides in ECR membrane domains of P1 and P2 vesicles, undergoes multiple rounds of temporal and spatial reorganization during priming and docking of both fusion partners. See Discussion for details.
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fig8: A model for the multistep remodeling of the peroxisome fusion machinery. The multicomponent peroxisome fusion machinery, which only transiently resides in ECR membrane domains of P1 and P2 vesicles, undergoes multiple rounds of temporal and spatial reorganization during priming and docking of both fusion partners. See Discussion for details.

Mentions: The results of this work and our published data (Titorenko and Rachubinski, 2000) suggest the following model for the multistep remodeling of the peroxisome fusion machinery in the membranes of P1 and P2 (Fig. 8). In unprimed P1 and P2, all identified essential components of this machinery, including Pex1p, Pex6p, PI(4)P-bp, PI(4,5)P2-bp, and GTP-bp, are attached to the cytosolic surface of ECR domains. Priming of fusion partners is initiated by the lateral movement of P1-associated Pex1p and P2-bound Pex6p from ECR domains to an ergosterol- and ceramide-poor portion of the membrane. This essential event in the process of activating fusion partners for subsequent docking includes at least three consecutive steps. The initial ergosterol-dependent step is followed by a PI(4)P-dependent step, which precedes a step that requires PI(4,5)P2. After their segregation from ECR domains, both P1-associated Pex1p and P2-bound Pex6p are released to the cytosol. Such release of both AAA ATPases from an ergosterol- and ceramide-poor portion of the membrane is mandatory for the priming of both fusion partners and includes two steps. The first step requires cytosolic proteins, whereas the next step is driven by ATP hydrolysis. Priming of P1 and P2 is followed by their docking. Docking of primed peroxisomal vesicles is a multistep process, which begins with the lateral movement of PI(4,5)P2-bp in the membranes of P1 and P2 from ECR domains to ergosterol- and ceramide-poor domains. This lateral movement of PI(4,5)P2-bp occurs in three consecutive steps. The first step needs ergosterol in the membranes of both fusion partners. The second step depends on Pex1p that resides in ECR domains of P2 vesicles. The third step requires GTP hydrolysis by GTPase(s), perhaps by GTP-bp in ECR domains of P1 vesicles. The docking-specific lateral movement of PI(4,5)P2-bp in the membranes of P1 and P2 is followed by the ergosterol-dependent relocation of P2-bound Pex1p from ECR domains to ergosterol- and ceramide-poor domains. After their lateral movement to ergosterol- and ceramide-poor portions of the membranes of both fusion partners, P1-associated PI(4,5)P2-bp and P2-bound PI(4,5)P2-bp and Pex1p are released to the cytosol. Such release of PI(4,5)P2-bp and Pex1p begins with a cytosol-dependent step, which is followed by a step that requires ATP hydrolysis. By the end of the docking process, PI(4)P-bp and GTP-bp remain in ECR domains of P1 and P2. The GTP-bp, together with calmodulin and a protein machinery that maintains the Ca2+ gradient across the peroxisomal membrane, is mandatory for the fusion of docked fusion partners (unpublished data). It remains to be established how the described remodeling of the peroxisome fusion machineries in the membranes of P1 and P2 changes the physical properties and topology of lipid bilayers in which these machineries operate, thereby triggering peroxisome docking. The exact nature of the changes in the membrane lipid bilayers of both fusion partners is currently being investigated.


Dynamic ergosterol- and ceramide-rich domains in the peroxisomal membrane serve as an organizing platform for peroxisome fusion.

Boukh-Viner T, Guo T, Alexandrian A, Cerracchio A, Gregg C, Haile S, Kyskan R, Milijevic S, Oren D, Solomon J, Wong V, Nicaud JM, Rachubinski RA, English AM, Titorenko VI - J. Cell Biol. (2005)

A model for the multistep remodeling of the peroxisome fusion machinery. The multicomponent peroxisome fusion machinery, which only transiently resides in ECR membrane domains of P1 and P2 vesicles, undergoes multiple rounds of temporal and spatial reorganization during priming and docking of both fusion partners. See Discussion for details.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171827&req=5

fig8: A model for the multistep remodeling of the peroxisome fusion machinery. The multicomponent peroxisome fusion machinery, which only transiently resides in ECR membrane domains of P1 and P2 vesicles, undergoes multiple rounds of temporal and spatial reorganization during priming and docking of both fusion partners. See Discussion for details.
Mentions: The results of this work and our published data (Titorenko and Rachubinski, 2000) suggest the following model for the multistep remodeling of the peroxisome fusion machinery in the membranes of P1 and P2 (Fig. 8). In unprimed P1 and P2, all identified essential components of this machinery, including Pex1p, Pex6p, PI(4)P-bp, PI(4,5)P2-bp, and GTP-bp, are attached to the cytosolic surface of ECR domains. Priming of fusion partners is initiated by the lateral movement of P1-associated Pex1p and P2-bound Pex6p from ECR domains to an ergosterol- and ceramide-poor portion of the membrane. This essential event in the process of activating fusion partners for subsequent docking includes at least three consecutive steps. The initial ergosterol-dependent step is followed by a PI(4)P-dependent step, which precedes a step that requires PI(4,5)P2. After their segregation from ECR domains, both P1-associated Pex1p and P2-bound Pex6p are released to the cytosol. Such release of both AAA ATPases from an ergosterol- and ceramide-poor portion of the membrane is mandatory for the priming of both fusion partners and includes two steps. The first step requires cytosolic proteins, whereas the next step is driven by ATP hydrolysis. Priming of P1 and P2 is followed by their docking. Docking of primed peroxisomal vesicles is a multistep process, which begins with the lateral movement of PI(4,5)P2-bp in the membranes of P1 and P2 from ECR domains to ergosterol- and ceramide-poor domains. This lateral movement of PI(4,5)P2-bp occurs in three consecutive steps. The first step needs ergosterol in the membranes of both fusion partners. The second step depends on Pex1p that resides in ECR domains of P2 vesicles. The third step requires GTP hydrolysis by GTPase(s), perhaps by GTP-bp in ECR domains of P1 vesicles. The docking-specific lateral movement of PI(4,5)P2-bp in the membranes of P1 and P2 is followed by the ergosterol-dependent relocation of P2-bound Pex1p from ECR domains to ergosterol- and ceramide-poor domains. After their lateral movement to ergosterol- and ceramide-poor portions of the membranes of both fusion partners, P1-associated PI(4,5)P2-bp and P2-bound PI(4,5)P2-bp and Pex1p are released to the cytosol. Such release of PI(4,5)P2-bp and Pex1p begins with a cytosol-dependent step, which is followed by a step that requires ATP hydrolysis. By the end of the docking process, PI(4)P-bp and GTP-bp remain in ECR domains of P1 and P2. The GTP-bp, together with calmodulin and a protein machinery that maintains the Ca2+ gradient across the peroxisomal membrane, is mandatory for the fusion of docked fusion partners (unpublished data). It remains to be established how the described remodeling of the peroxisome fusion machineries in the membranes of P1 and P2 changes the physical properties and topology of lipid bilayers in which these machineries operate, thereby triggering peroxisome docking. The exact nature of the changes in the membrane lipid bilayers of both fusion partners is currently being investigated.

Bottom Line: We describe unusual ergosterol- and ceramide-rich (ECR) domains in the membrane of yeast peroxisomes.Several key features of these detergent-resistant domains, including the nature of their sphingolipid constituent and its unusual distribution across the membrane bilayer, clearly distinguish them from well characterized detergent-insoluble lipid rafts in the plasma membrane.A distinct set of peroxisomal proteins, including two ATPases, Pex1p and Pex6p, as well as phosphoinositide- and GTP-binding proteins, transiently associates with the cytosolic face of ECR domains.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Concordia University, Montreal, Quebec H4B 1R6, Canada.

ABSTRACT
We describe unusual ergosterol- and ceramide-rich (ECR) domains in the membrane of yeast peroxisomes. Several key features of these detergent-resistant domains, including the nature of their sphingolipid constituent and its unusual distribution across the membrane bilayer, clearly distinguish them from well characterized detergent-insoluble lipid rafts in the plasma membrane. A distinct set of peroxisomal proteins, including two ATPases, Pex1p and Pex6p, as well as phosphoinositide- and GTP-binding proteins, transiently associates with the cytosolic face of ECR domains. All of these proteins are essential for the fusion of the immature peroxisomal vesicles P1 and P2, the earliest intermediates in a multistep pathway leading to the formation of mature, metabolically active peroxisomes. Peroxisome fusion depends on the lateral movement of Pex1p, Pex6p, and phosphatidylinositol-4,5-bisphosphate-binding proteins from ECR domains to a detergent-soluble portion of the membrane, followed by their release to the cytosol. Our data suggest a model for the multistep reorganization of the multicomponent peroxisome fusion machinery that transiently associates with ECR domains.

Show MeSH
Related in: MedlinePlus