A new approach for the AAA peroxin research

AAA蛋白家族的两种过氧化物酶Pexlp和Pex6p分别负责过氧化物酶体生物发生障碍（pbd），如补体组1 （CG1）和CG4的Zellweger综合征。这些过氧化物蛋白被Pex26p招募到过氧化物酶体膜上，并被认为参与了Pex5p过氧化物酶体的输出，Pex5p是PTS1基质蛋白的可溶性再循环受体。此外，我们最近报道了Pexlp部分存在于细胞质中，而不形成Pexlp- pex6p - pex26p复合物。然而，Pex5p循环系统的分子机制尚不清楚。因此，我们研究了AAA过氧化物酶在过氧化物酶体膜和细胞质中的作用。共免疫沉淀和拉下实验表明，Pex26p能够结合与Pex5p相关的Pex14p。Pex26p-Pex14p复合物以atp依赖的方式被peexlp和peex6p解离。HEK293细胞胞浆部分和重组蛋白的Blue-Native凝胶分析表明，Pex1p主要处于同源三聚体中。在CHO-K1细胞的Pex5p低聚物结构分析中，细胞质中Pex5p显示为二聚体和单体形式，尽管来自pex1p缺失的ZP107细胞的细胞质中Pex5p主要以单体形式存在。综上所述，Pexlp-Pex6p复合物可能调节Pex26p和Pex14p的相互作用，可能从Pex14p中释放peex5p。此外，Pex5p的同型三聚体被认为参与了细胞质Pex5p从单体到二聚体的转化。我们讨论了AAA过氧化物酶在过氧化物酶体蛋白输入和Pex5p循环中的顺序作用。

Two peroxins, Pexlp and Pex6p, of the AAA protein family are responsible for peroxisome biogenesis disorders (PBDs) such as Zellweger syndrome of complementation group 1 (CG1) and CG4, respectively. These peroxins were recruited to peroxisomal membrane by Pex26p and suggested to be involved in the export from peroxisomes of Pex5p, the soluble recycling receptor for PTS1 matrix proteins. Furthermore, we recently reported that Pexlp was present partly in cytosol without forming a Pexlp-Pex6p-Pex26p complex. However, the molecular mechanism of the recycling system for Pex5p is not well understood. Therefore we investigated the role of AAA peroxins on peroxisomal membrane as well as in the cytosol. Co-immunoprecipitation and pull-down assays showed that Pex26p is competent to bind to Pex14p associated with Pex5p. The Pex26p-Pex14p complex was dissociated by Pexlp and Pex6p in an ATP-dependent manner. Blue-Native gel analysis of the cytosolic fraction from HEK293 cells and recombinant protein showed that Pex1p is mostly in a homo-trimer. In the assays for Pex5p oligomer structure in CHO-K1 cells, cytosolic Pex5p showed both dimer and monomer forms, although cytosolic Pex5p from Pex1p-deficient ZP107 cells was predominantly in a monomer form. Taken together, Pexlp-Pex6p complexes are likely to modulate the interaction of Pex26p and Pex14p, presumably releasing Pex5p from Pex14p. Furthermore, homo-trimer of Pexlp complexes were suggested to be involved in the conversion from a monomer to a dimer of cytosolic Pex5p. We discussed the sequential role of AAA peroxins in peroxisomal protein import and Pex5p recycling.