Molecular and Cell Biology, International Graduate Program, Academia Sinica and Graduate Institute of Life Science, National Defense Medical Center, Taipei, Taiwan.
Institute of Molecular Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 11529, Taiwan.
Plant J. 2019 Jul;99(1):128-143. doi: 10.1111/tpj.14316. Epub 2019 Apr 12.
In mammals and yeast, tail-anchored (TA) membrane proteins destined for the post-translational pathway are safely delivered to the endoplasmic reticulum (ER) membrane by a well-known targeting factor, TRC40/Get3. In contrast, the underlying mechanism for translocation of TA proteins in plants remains obscure. How this unique eukaryotic membrane-trafficking system correctly distinguishes different subsets of TA proteins destined for various organelles, including mitochondria, chloroplasts and the ER, is a key question of long standing. Here, we present crystal structures of algal ArsA1 (the Get3 homolog) in a distinct nucleotide-free open state and bound to adenylyl-imidodiphosphate. This approximately 80-kDa protein possesses a monomeric architecture, with two ATPase domains in a single polypeptide chain. It is capable of binding chloroplast (TOC34 and TOC159) and mitochondrial (TOM7) TA proteins based on features of its transmembrane domain as well as the regions immediately before and after the transmembrane domain. Several helices located above the TA-binding groove comprise the interlocking hook-like motif implicated by mutational analyses in TA substrate recognition. Our data provide insights into the molecular basis of the highly specific selectivity of interactions of algal ArsA1 with the correct sets of TA substrates before membrane targeting in plant cells.
在哺乳动物和酵母中，尾部锚定（TA）膜蛋白通过一种众所周知的靶向因子 TRC40/Get3 被安全地递送到内质网（ER）膜。相比之下，植物中 TA 蛋白易位的潜在机制仍然不清楚。这个独特的真核膜运输系统如何正确地区分不同亚类的 TA 蛋白，这些蛋白分别定位于不同的细胞器，包括线粒体、叶绿体和 ER，是一个长期存在的关键问题。在这里，我们展示了藻类 ArsA1（Get3 同源物）在独特的无核苷酸开放状态下与腺苷酰-亚咪唑二磷酸结合的晶体结构。这种大约 80kDa 的蛋白质具有单体结构，在单个多肽链中包含两个 ATP 酶结构域。它能够结合叶绿体（TOC34 和 TOC159）和线粒体（TOM7）TA 蛋白，这是基于其跨膜结构域以及跨膜结构域前后的区域的特征。位于 TA 结合槽上方的几个螺旋构成了由突变分析暗示的互锁钩状模体，该模体在 TA 底物识别中起作用。我们的数据提供了关于藻类 ArsA1 在植物细胞中进行膜靶向之前与正确的 TA 底物相互作用的高度特异性选择性的分子基础的见解。
