PEX11 proteins attract Mff and human Fis1 to coordinate peroxisomal fission.

Fission of membrane-bound organelles requires membrane remodeling processes to enable and facilitate the assembly of the scission machinery. Proteins of the PEX11 family were shown to act as membrane elongation factors during peroxisome proliferation. Furthermore, through interaction with fission factors these proteins coordinate progression of membrane scission. Using a biochemical approach, we determined the membrane topology of PEX11γ, one of the three human PEX11 proteins. Analysis of PEX11γ mutants, which localize to peroxisomes, revealed essential domains for membrane elongation including an amphipathic region and regulatory sequences thereof. Through pegylation assays and in vivo studies, we establish that the PEX11γ sequence includes two membrane-anchored domains, which dock an amphipathic region onto the peroxisomal membrane thereby regulating its elongation. The interaction profile of wild-type and mutant PEX11γ and reveals a rearrangement between homo- and heterodimerization and association with fission factors. We also demonstrate the presence of the mitochondrial fission factor Mff on peroxisomes and its interaction with PEX11 proteins. Our data reveal several features of the molecular mechanism of peroxisome proliferation in mammalian cells: (1) PEX11γ is required and acts in coordination with at least one of the other PEX11 proteins to protrude the peroxisomal membrane; (2) PEX11 proteins attract both Mff and human Fis1 (hFis1) to their site of action; and (3) the concerted interaction of PEX11 proteins provides spatiotemporal control for growth and division of peroxisomes.