Peroxisome - Peroxisome Assembly

Peroxisome Assembly

Peroxisomes can be derived from the endoplasmic reticulum and replicate by fission. Peroxisome matrix proteins are translated in the cytoplasm prior to import. Specific amino acid sequences (PTS or peroxisomal targeting signal) at the C-terminus (PTS1) or N-terminus (PTS2) of peroxisomal matrix proteins signals them to be imported into the organelle. There are at least 32 known peroxisomal proteins, called peroxins, which participate in the process of peroxisome assembly. Proteins do not have to unfold to be imported into the peroxisome. The protein receptors, the peroxins PEX5 and PEX7, accompany their cargoes (containing a PTS1 or a PTS2 amino acid sequence, respectively) all the way into the peroxisome where they release the cargo and then return to the cytosol - a step named recycling. A model describing the import cycle is referred to as the extended shuttle mechanism. There is now evidence that ATP hydrolysis is required for the recycling of receptors to the cytosol. Also, ubiquitination appears to be crucial for the export of PEX5 from the peroxisome, to the cytosol.