Self-Interaction of Human Pex11pβ during Peroxisomal Growth and Division

Pex11 proteins are involved in membrane elongation and division processes associated with the multiplication of peroxisomes. Human Pex11p beta has recently been linked to a new disorder affecting peroxisome morphology and dynamics. Here, we have analyzed the exact membrane topology of Pex11p beta. Studies with an epitope-specific antibody and protease protection assays show that Pex11p beta is an integral membrane protein with two transmembrane domains flanking an internal region exposed to the peroxisomal matrix and N-and C-termini facing the cytosol. A glycine-rich internal region within Pex11p beta is dispensable for peroxisome membrane elongation and division. However, we demonstrate that an amphipathic helix (Helix 2) within the first N-terminal 40 amino acids is crucial for membrane elongation and self-interaction of Pex11p beta. Interestingly, we find that Pex11p beta self-interaction strongly depends on the detergent used for solubilization. We also show that N-terminal cysteines are not essential for membrane elongation, and that putative N-terminal phosphorylation sites are dispensable for Pex11p beta function. We propose that self-interaction of Pex11p beta regulates its membrane deforming activity in conjunction with membrane lipids.