Plastic production has been rising consistently in the last 30 years and with it, the presence of plastic particles in the environment. A decrease in size often increases the bioavailability and reactivity of the particles. In this study the impact of polystyrene (PS; 22 nm) and polymethylmethacrylate (PMMA; 32 nm) nanoparticles on zebrafish embryo-larval stages was assessed by studying mortality, hatching, morphological features, and biochemical endpoints (associated with neurotransmission, antioxidant status and oxidative damage, and energy metabolism) after 96 h exposure, and swimming behavior after 120 h exposure. Organisms exposed to PMMA nanoparticles exhibited higher mortality and pericardial edema than those exposed to PS nanoparticles but displayed less effects on swimming behavior. Biochemical endpoints were altered to a higher degree in organisms exposed to PS nanoparticles (acetylcholinesterase, glutathione S-transferase and catalase activities) but higher peroxidative damage was found after exposure to lower concentrations of PMMA nanoparticles. Both types of nanoparticles affected energy metabolism with higher levels of glycogen found in animals exposed to PS nanoparticles. The use of integrated biomarker response index confirmed that PS nanoparticles had a higher impact on biochemical endpoints of zebrafish.

Pex11 proteins are involved in membrane elongation and division processes associated with the multiplication of peroxisomes. Human Pex11pβ has recently been linked to a new disorder affecting peroxisome morphology and dynamics. Here, we have analyzed the exact membrane topology of Pex11pβ. Studies with an epitope-specific antibody and protease protection assays show that Pex11pβ 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 Pex11pβ 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 Pex11pβ. Interestingly, we find that Pex11pβ 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 Pex11pβ function. We propose that self-interaction of Pex11pβ regulates its membrane deforming activity in conjunction with membrane lipids.