Murphy Mary A, Phillipson Belinda A, Baker Alison, Mullen Robert T
Department of Botany, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Plant Physiol. 2003 Oct;133(2):813-28. doi: 10.1104/pp.103.027870. Epub 2003 Sep 4.
Using a combination of in vivo and in vitro assays, we characterized the sorting pathway and molecular targeting signal for the Arabidopsis 22-kD peroxisome membrane protein (PMP22), an integral component of the membrane of all peroxisomes in the mature plant. We show that nascent PMP22 is sorted directly from the cytosol to peroxisomes and that it is inserted into the peroxisomal boundary membrane with its N- and C-termini facing the cytosol. This direct sorting of PMP22 to peroxisomes contrasts with the indirect sorting reported previously for cottonseed (Gossypium hirsutum) ascorbate peroxidase, an integral PMP that sorts to peroxisomes via a subdomain of the endoplasmic reticulum. Thus, at least two different sorting pathways for PMPs exist in plant cells. At least four distinct regions within the N-terminal one-half of PMP22, including a positively charged domain present in most peroxisomal integral membrane-destined proteins, functions in a cooperative manner in efficient peroxisomal targeting and insertion. In addition, targeting with high fidelity to peroxisomes requires all four membrane-spanning domains in PMP22. Together, these results illustrate that the PMP22 membrane peroxisomal targeting signal is complex and that different elements within the signal may be responsible for mediating unique aspects of PMP22 biogenesis, including maintaining the solubility before membrane insertion, targeting to peroxisomes, and ensuring proper assembly in the peroxisomal boundary membrane.
通过结合体内和体外试验，我们对拟南芥22-kD过氧化物酶体膜蛋白（PMP22）的分选途径和分子靶向信号进行了表征，该蛋白是成熟植物中所有过氧化物酶体膜的一个组成成分。我们发现新生的PMP22直接从细胞质分选至过氧化物酶体，并且它以N端和C端面向细胞质的方式插入过氧化物酶体界膜。PMP22直接分选至过氧化物酶体与之前报道的棉籽（陆地棉）抗坏血酸过氧化物酶的间接分选形成对比，棉籽抗坏血酸过氧化物酶是一种整合型PMP，它通过内质网的一个亚结构域分选至过氧化物酶体。因此，植物细胞中存在至少两种不同的PMP分选途径。PMP22 N端一半区域内至少有四个不同区域，包括大多数定位于过氧化物酶体整合膜的蛋白中存在的一个带正电荷结构域，它们以协同方式在高效的过氧化物酶体靶向和插入过程中发挥作用。此外，高保真靶向过氧化物酶体需要PMP22中的所有四个跨膜结构域。这些结果共同表明，PMP22膜过氧化物酶体靶向信号很复杂，信号内的不同元件可能负责介导PMP22生物合成的独特方面，包括在膜插入前保持溶解性、靶向过氧化物酶体以及确保在过氧化物酶体界膜中正确组装。
