Phosphoinositide- and GTP hydrolysis-dependent segregation of two AAA family ATPases from ergosterol- and ceramide-rich membrane domains is required for membrane fusion.
Tatiana Boukh-Viner, Tong Guo, Robert Kyskan, Svetlana Milijevic, Christopher Gregg, Andre Cerracchio, Sandra Haile, Alex Alexandrian, Vivianne Wong, Jonathan Solomon, Vladimir Titorenko
Department of Biology, Concordia University, 7141 Sherbrooke Str., Montreal, PQ, H4B 1R6, Canada
We have reconstituted in vitro the fusion of small peroxisomal vesicles P1 and P2 from the yeast Yarrowia lipolytica. The fusion yields a larger peroxisome, P3. Peroxisome fusion is a multistep process that includes priming, docking and fusion events. It depends on numerous peroxisome-associated components previously implicated in a variety of intracellular signal transduction pathways, including detergent-resistant membrane domains called lipid rafts. Lipid rafts in the membranes of unprimed P1 and P2 are enriched in ergosterol and ceramide and contain at least two essential components of the peroxisomal fusogenic machinery, the ATPases of the AAA protein family Pex1p and Pex6p whose deficiency is responsible for the vast majority of the human peroxisome biogenesis disorders. During peroxisome priming and docking, Pex1p and Pex6p relocate from the lipid raft to a detergent-soluble membrane domain, in an ergosterol-, PI(4)P-, PI(4,5)P2-, monomeric GTPase- and ATP hydrolysis-dependent manner. The lateral movement of Pex1p and Pex6p from lipid rafts to detergent-soluble membrane domains is mandatory for the release of Pex1p and Pex6p from the membrane surface to the cytosol and plays a pivotal role in membrane fusion. Our data suggest a model for the dynamics of temporally and spatially regulated interactions between various components of lipid raft-associated signal transduction cascades that operate during peroxisome fusion.
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