Editing Peroxisome (section)

== Peroxisome assembly ==
Peroxisomes are derived from the [[smooth endoplasmic reticulum]] under certain experimental conditions and replicate by membrane growth and division out of pre-existing organelles.<ref name="pmid16009135">{{cite journal | vauthors = Hoepfner D, Schildknegt D, Braakman I, Philippsen P, Tabak HF | title = Contribution of the endoplasmic reticulum to peroxisome formation | journal = Cell | volume = 122 | issue = 1 | pages = 85–95 | date = July 2005 | pmid = 16009135 | doi = 10.1016/j.cell.2005.04.025 | hdl = 1874/9833 | s2cid = 18837009 | hdl-access = free }}</ref><ref>{{cite journal | vauthors = Schrader M, Costello JL, Godinho LF, Azadi AS, Islinger M | title = Proliferation and fission of peroxisomes - An update | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1863 | issue = 5 | pages = 971–83 | date = May 2016 | pmid = 26409486 | doi = 10.1016/j.bbamcr.2015.09.024 | doi-access = free | hdl = 10871/18323 | hdl-access = free }}</ref><ref>{{cite journal | vauthors = Lazarow PB, Fujiki Y | title = Biogenesis of peroxisomes | journal = Annual Review of Cell Biology | volume = 1 | issue = 1 | pages = 489–530 | date = Nov 1985 | pmid = 3916321 | doi = 10.1146/annurev.cb.01.110185.002421 }}</ref> 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 signal them to be imported into the organelle by a targeting factor. There are currently 36 known proteins involved in peroxisome biogenesis and maintenance, called [[peroxin]]s,<ref name="pmid17050007">{{cite journal | vauthors = Saleem RA, Smith JJ, Aitchison JD | title = Proteomics of the peroxisome | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1763 | issue = 12 | pages = 1541–51 | date = December 2006 | pmid = 17050007 | pmc = 1858641 | doi = 10.1016/j.bbamcr.2006.09.005 }}</ref> which participate in the process of peroxisome assembly in different organisms. In mammalian cells, there are 13 characterized peroxins. In contrast to protein import into the endoplasmic reticulum (ER) or mitochondria, proteins do not need to be unfolded to be imported into the peroxisome lumen. The matrix protein import receptors, the peroxins [[PEX5]] and [[PEX7]], accompany their cargoes (containing a PTS1 or a PTS2 amino acid sequence, respectively) all the way to the peroxisome where they release the cargo into the peroxisomal matrix and then return to the [[cytosol]] – a step named ''recycling''. A special way of peroxisomal protein targeting is called piggybacking. Proteins transported by this unique method do not have a canonical PTS but bind on a PTS protein to be transported as a complex.<ref>{{Cite journal|last=Thoms|first=Sven|date=Nov 2015|title=Import of proteins into peroxisomes: piggybacking to a new home away from home|journal=Open Biology|volume=5|issue=11|pages=150148|doi=10.1098/rsob.150148|pmid=26581572|pmc=4680570|issn=2046-2441}}</ref> A model describing the import cycle is referred to as the ''extended shuttle mechanism''.<ref name="pmid11336669">{{cite journal | vauthors = Dammai V, Subramani S | title = The human peroxisomal targeting signal receptor, Pex5p, is translocated into the peroxisomal matrix and recycled to the cytosol | journal = Cell | volume = 105 | issue = 2 | pages = 187–96 | date = April 2001 | pmid = 11336669 | doi = 10.1016/s0092-8674(01)00310-5 | s2cid = 18873642 | doi-access = free | citeseerx = 10.1.1.385.9484 }}</ref> There is now evidence that ATP hydrolysis is required for the recycling of receptors to the cytosol. Also, [[ubiquitination]] is crucial for the export of PEX5 from the peroxisome to the cytosol. The biogenesis of the peroxisomal membrane and the insertion of peroxisomal membrane proteins (PMPs) requires the peroxins PEX19, PEX3, and PEX16. PEX19 is a PMP receptor and chaperone, which binds the PMPs and routes them to the peroxisomal membrane, where it interacts with PEX3, a peroxisomal integral membrane protein. PMPs are then inserted into the peroxisomal membrane.

The degradation of peroxisomes is called pexophagy.<ref>{{cite journal | vauthors = Eberhart T, Kovacs WJ | title = Pexophagy in yeast and mammals: an update on mysteries | journal = Histochemistry and Cell Biology | volume = 150 | issue = 5 | pages = 473–488 | date = November 2018 | pmid = 30238155 | doi = 10.1007/s00418-018-1724-3 | hdl = 20.500.11850/302080 | s2cid = 52307878 | hdl-access = free }}</ref>