OEP61 is a chaperone receptor at the plastid outer envelope.
OEP61 is a chaperone receptor at the plastid outer envelope.
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DOI：
10.1042/bj20110448
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发表时间：
2011-08
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通讯作者：
O. von Loeffelholz;V. Kriechbaumer;R. Ewan;Rafał Jończyk;S. Lehmann;Jason C. Young;B. Abell
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作者：
O. von Loeffelholz;V. Kriechbaumer;R. Ewan;Rafał Jończyk;S. Lehmann;Jason C. Young;B. Abell
在细胞核中编码的叶绿体前体蛋白依赖于它们的靶向序列来传递到叶绿体中。有不同的途径到叶绿体外包膜，但一个共同的主题是分子伴侣的参与。Hsp90（热休克蛋白90）通过其受体Toc64传递前体，Toc64将前体转移到外包膜的核心转位酶。在本文中，我们在拟南芥OEP61中发现了一个与Toc64具有共同特征的未知蛋白，可能为叶绿体提供了另一种途径。序列分析表明，OEP61具有一个能够结合分子伴侣的钳型TPR（四肽重复）结构域和一个c端跨膜结构域。系统发育比较表明，OEP61的TPR结构域与Toc64家族的TPR结构域序列相似。在所有植物组织中均检测到mRNA和蛋白的表达，并通过显微镜和体外导入实验证明了叶绿体外包膜的定位。结合实验表明，OEP61通过其TPR箝位域与热休克蛋白70 （Hsp70）特异性相互作用。此外，OEP61通过叶绿体前体的靶向序列选择性识别叶绿体前体，并且OEP61的可溶性形式抑制叶绿体靶向。因此，我们认为OEP61是叶绿体外包膜上的一种新的伴侣受体，介导hsp70依赖蛋白靶向叶绿体。
Chloroplast precursor proteins encoded in the nucleus depend on their targeting sequences for delivery to chloroplasts. There exist different routes to the chloroplast outer envelope, but a common theme is the involvement of molecular chaperones. Hsp90 (heat-shock protein 90) delivers precursors via its receptor Toc64, which transfers precursors to the core translocase in the outer envelope. In the present paper, we identify an uncharacterized protein in Arabidopsis thaliana OEP61 which shares common features with Toc64, and potentially provides an alternative route to the chloroplasts. Sequence analysis indicates that OEP61 possesses a clamp-type TPR (tetratricopeptide repeat) domain capable of binding molecular chaperones, and a C-terminal TMD (transmembrane domain). Phylogenetic comparisons show sequence similarities between the TPR domain of OEP61 and those of the Toc64 family. Expression of mRNA and protein was detected in all plant tissues, and localization at the chloroplast outer envelope was demonstrated by a combination of microscopy and in vitro import assays. Binding assays show that OEP61 interacts specifically with Hsp70 (heat-shock protein 70) via its TPR clamp domain. Furthermore, OEP61 selectively recognizes chloroplast precursors via their targeting sequences, and a soluble form of OEP61 inhibits chloroplast targeting. We therefore propose that OEP61 is a novel chaperone receptor at the chloroplast outer envelope, mediating Hsp70-dependent protein targeting to chloroplasts.