Molecular mechanisms for recognition and transport of proteins by a protein complex exists in peroxisomal membrane

过氧化物酶体蛋白通过识别称为PTS1和PTS2的两种蛋白质靶向信号之一从细胞质转运到过氧化物酶体。去年，我们发现了两个可以捕获PTS 1和PTS2的受体（Pex5p和Pex7p），并显示了Pex5p和Pex7p之间的蛋白-蛋白相互作用，以及Pex5p和过氧化物酶体膜蛋白Pex14p之间的蛋白相互作用。本财年，我们通过RNA干扰技术生产了抑制pex5和pex7基因表达的转基因植物。对这些转基因植物的分析显示了以下两点。(1) Pex5p的缺失抑制了pts1和pts2蛋白向过氧化物酶体的输入。不含Pex5p的转基因植株的glyoxysomes和叶片过氧化物酶体的功能均存在缺陷。(2) Pex7p的缺失只抑制含有pts2蛋白的输入。不含Pex7p的转基因植株仅在glyoxysomal功能上存在缺陷。从这些观察中，我们得出结论，Pex5p和Pex7p在细胞质中形成受体-货物复合物，并且受体-货物复合物被Pex5p和过氧化物酶体膜蛋白Pex14p之间的蛋白质-蛋白质相互作用所捕获。

Peroxisomal proteins are transported from the cytosol into peroxisomes by a recognition of one of the two protein targeting signals called PTS1 and PTS2. Last year, we identified two receptors (Pex5p and Pex7p) that can capture PTS 1 and PTS2, and showed protein-protein interaction between Pex5p and Pex7p, as well as Pex5p and a peroxisomal membrane protein, Pex14p. In this fiscal year, we produced transgenic plants that suppressed PEX5-and PEX7-gene expression by RNA interference technology. Analyses of these transgenic plants showed following 2 points. (1) Loss of Pex5p inhibits the import of both PTS1-and PTS2-containing proteins into peroxisomes. The transgenic plants without Pex5p showed defects in functions of both glyoxysomes and leaf peroxisomes. (2) Loss of Pex7p inhibits the import of only PTS2-containing proteins. The transgenic plants without Pex7p showed defect only in glyoxysomal function. From these observation, we concluded that Pex5p and Pex7p form a receptor-cargo complex in the cytosol, and the receptor-cargo complex is captured by the protein-protein interaction between Pex5p and the peroxisomal membrane protein, Pex14p.