Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673, Korea.
Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673, Korea.
Mol Plant. 2019 Jul 1;12(7):951-966. doi: 10.1016/j.molp.2019.03.003. Epub 2019 Mar 16.
Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively. However, how these highly similar signal sequences confer the protein import specificity remains elusive. Here, we show that mitochondrial- or chloroplast-specific import involves two distinct steps, specificity determination and translocation across envelopes, which are mediated by the N-terminal regions and functionally interchangeable C-terminal regions, respectively, of transit peptides and presequences. A domain harboring multiple-arginine and hydrophobic sequence motifs in the N-terminal regions of presequences was identified as the mitochondrial specificity factor. The presence of this domain and the absence of arginine residues in the N-terminal regions of otherwise common targeting signals confers specificity of protein import into mitochondria and chloroplasts, respectively. AtToc159, a chloroplast import receptor, also contributes to determining chloroplast import specificity. We propose that common ancestral sequences were functionalized into mitochondrial- and chloroplast-specific signal sequences by the presence and absence, respectively, of multiple-arginine and hydrophobic sequence motifs in the N-terminal region.
植物拥有两种类型的共生细胞器，叶绿体和线粒体。转运肽和前导序列分别作为蛋白质特异性导入叶绿体和线粒体的信号序列。然而，这些高度相似的信号序列如何赋予蛋白质导入的特异性仍然难以捉摸。在这里，我们表明，线粒体或叶绿体的特异性导入涉及两个不同的步骤，特异性确定和跨膜转运，分别由转运肽和前导序列的 N 端区域和功能可互换的 C 端区域介导。在前导序列的 N 端区域中鉴定出一个包含多个精氨酸和疏水性序列基序的结构域，作为线粒体特异性因子。该结构域的存在以及 N 端区域中精氨酸残基的缺失，分别赋予了蛋白质导入线粒体和叶绿体的特异性。叶绿体导入受体 AtToc159 也有助于确定叶绿体导入的特异性。我们提出，共同的祖先序列通过 N 端区域中多精氨酸和疏水性序列基序的存在和缺失，分别被功能化成为线粒体和叶绿体特异性的信号序列。
