From the Organelle Biogenesis and Function Group and.
J Biol Chem. 2013 Oct 4;288(40):29151-9. doi: 10.1074/jbc.M113.487140. Epub 2013 Aug 20.
Peroxisomal matrix proteins are synthesized on cytosolic ribosomes and post-translationally targeted to the organelle by PEX5, the peroxisomal shuttling receptor. The pathway followed by PEX5 during this process is known with reasonable detail. After recognizing cargo proteins in the cytosol, the receptor interacts with the peroxisomal docking/translocation machinery, where it gets inserted; PEX5 is then monoubiquitinated, extracted back to the cytosol and, finally, deubiquitinated. However, despite this information, the exact step of this pathway where cargo proteins are translocated across the organelle membrane is still ill-defined. In this work, we used an in vitro import system to characterize the translocation mechanism of a matrix protein possessing a type 1 targeting signal. Our results suggest that translocation of proteins across the organelle membrane occurs downstream of a reversible docking step and upstream of the first cytosolic ATP-dependent step (i.e. before ubiquitination of PEX5), concomitantly with the insertion of the receptor into the docking/translocation machinery.
过氧化物酶体基质蛋白在细胞质核糖体上合成,然后通过过氧化物酶体易位受体 PEX5 进行翻译后靶向细胞器。在此过程中,PEX5 所遵循的途径已经有了相当详细的了解。在细胞质中识别货物蛋白后,受体与过氧化物酶体对接/易位机制相互作用,在那里它被插入;然后 PEX5 被单泛素化,被提取回细胞质,最后去泛素化。然而,尽管有这些信息,货物蛋白穿过细胞器膜的这个途径的确切步骤仍然没有明确界定。在这项工作中,我们使用体外导入系统来描述具有 1 型靶向信号的基质蛋白的易位机制。我们的结果表明,蛋白质穿过细胞器膜的易位发生在可逆对接步骤的下游和第一个细胞质 ATP 依赖性步骤(即在 PEX5 泛素化之前),同时伴随着受体插入对接/易位机制。