peroxisomes

Peroxisomes are cytoplasmic organelles found in animal cells, especially liver, kidney and brain cells. They are the site of a variety of anabolic and catabolic pathways: oxidation and plasmalogen synthesis are two fundamental pathways localized there.

The peroxisomal oxidation enzymes are distinct from the mitochondrial system.

Oxidation of straight-chain very-long-chain fatty acid (VLCFA) requires the enzymes very-long-chain acyl CoA synthetase, acyl CoA oxidase, D-bifunctional protein (enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase), and peroxisomal ketothiolase.

The defect in peroxisomal fatty acid oxidation accounts for the increase in VLCFA straight and branched-chain fatty acids.

At least 29 special proteins (peroxins) encoded by PEXs genes are required for peroxisome membrane biogenesis, fission, and protein import to form competent organelles.

The biogenesis of membranes is not well understood, but mutations in three human PEX genes (PEX3, 16, and 19) are associated with an absence of any peroxisome membrane structures.

The remaining proteins encoded by known PEX genes (PEX1, 6, 26, 10, 12, 2, 5, 13 and 14) most probably contribute to the machinery required for matrix protein import.

Functions

 Peroxisomes import folded, even oligomeric, proteins, which distinguishes the peroxisomal translocation machinery from the well-characterized translocons of other organelles.

 Like other subcellular organelles, peroxisomes divide and segregate to daughter cells during cell division, but this organelle can also proliferate or be degraded in response to environmental cues.

Although the mechanisms and genes involved in these processes are still under active investigation, an important player in peroxisome proliferation is a dynamin-related protein (DRP) that is recruited to the organelle membrane by a DRP receptor.

Related DRPs also function in the division of mitochondria and chloroplasts. Many other proteins and signals regulate peroxisome division and proliferation.

Peroxisomes are a dynamic compartment in almost all eukaryotic cells and have diverse metabolic roles in response to environmental changes and cellular demands. The accompanying changes in enzyme content or abundance of peroxisomes are accomplished by dynamically operating membrane- and matrix-protein transport machineries.

Pathology

 peroxisomes biogenesis disorders (MIM.601359)
 peroxisomal proliferation and maintenance
 insertion of peroxisomal membrane proteins
 compartmentalization of peroxisomal matrix proteins
 selective degradation of peroxisomes via pexophagy

See also

 peroxisome proliferator-activated receptors (PPARs)

References

 Platta HW, Erdmann R. Peroxisomal dynamics. Trends Cell Biol. 2007 Oct;17(10):474-84. PMID: 17913497

 Yan M, Rayapuram N, Subramani S. The control of peroxisome number and size during division and proliferation. Curr Opin Cell Biol. 2005 Aug;17(4):376-83. PMID: 15978793

 Erdmann R, Schliebs W. Peroxisomal matrix protein import: the transient pore model. Nat Rev Mol Cell Biol. 2005 Sep;6(9):738-42. PMID: 16103872

 Titorenko VI, Rachubinski RA. The life cycle of the peroxisome. Nat Rev Mol Cell Biol. 2001 May;2(5):357-68. PMID: 11331910

 Titorenko VI, Rachubinski RA. Dynamics of peroxisome assembly and function. Trends Cell Biol. 2001 Jan;11(1):22-29. PMID: 11146295

 Pap EH, Dansen TB, Wirtz KW. Peptide-based targeting of fluorophores to peroxisomes in living cells. Trends Cell Biol. 2001 Jan;11(1):10-12. PMID: 11146278