Peroxisomes are single-membrane bound organelles present in virtually all eukaryotic cells. They are involved in numerous catabolic and anabolic pathways, including beta-oxidation of very long chain fatty acids, metabolism of hydrogen peroxide, plasmalogen biosynthesis and bile acid synthesis. The Peroxin gene family, which includes more than 20 members, is required for peroxisome biogenesis. Peroxin 5R, also known as PEX5-related protein or Peroxisome biogenesis factor 5-like, is a 626 amino acid protein that is mainly expressed in brain, with some expression in testis and pancreas. Peroxin 5R contains five TPR repeats, which enable protein-protein interactions and assembly of large multiprotein complexes. There are three isoforms of Peroxin 5R that are produced as a result of alternative splicing events. These isoforms bind C-terminal peroxisome-targeting signals in a similar manner to Peroxin-5. Peroxin 5R interacts with Rab 8b, possibly playing a role in vesicular trafficking and neurotransmitter release.