It is unclear how the long isoform of PEX5 (PEX5L) and the s...

created [InstanceEdit:9033618] May, Bruce, 2017-12-23
dbId 9033620
displayName It is unclear how the long isoform of PEX5 (PEX5L) and the s...
modified [InstanceEdit:9038630] May, Bruce, 2018-03-12
schemaClass Summation
text It is unclear how the long isoform of PEX5 (PEX5L) and the short isoform of PEX5 (PEX5S) are generated. A current hypothesis suggests alternative mRNA splicing. Both isoforms can bind the peroxisome targeting signal 1 (PTS1) located at the C-terminus of most of the proteins that are targeted to the peroxisomal matrix (Dodt et al. 1995, Fransen et al. 1995, Wiemer et al. 1995, Gatto et al. 2000, Brocard et al. 2003, Gatto et al. 2003, Harper et al. 2003, Ghosh and Berg 2010, Freitas et al. 2011, Okumoto et al. 2011). PTS1 typically contains Ser-Lys-Leu (SKL) at the C-terminus but substantial variation in sequences and affinities for PEX5 are observed and upstream residues can modulate binding to PEX5 (Lametschwandtner et al. 1998, Ghosh and Berg 2010, reviewed in Brocard and Hartig 2006).
A minority of peroxisomal matrix proteins contain PTS2. While the PEX5S isoform binds proteins containing PTS1, the PEX5L isoform binds either proteins containing PTS1 or PEX7 bound to proteins containing PTS2 (Braverman et al. 1998). Some proteins appear to be imported as oligomers, however this is rather inefficient as PEX5 appears to have a preference for monomeric substrates (Otera and Fujiki 2012, Freitas et al. 2011, Freitas et al. 2015, also inferred from mouse homologs). Mutations in PEX5 cause defects in peroxisomal import and comprise complementation group 2 of peroxisomal biogenesis disorders (also called Zellweger spectrum disorders) (Dodt et al. 1995, Wiemer et al. 1995). A specific mutation affecting only the PEX5L isoform is the cause of rhizomelic chondrodysplasia punctate type 5 (Barøy et al. 2015).
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