Institute for Molecular Biosciences, Goethe University Frankfurt am Main, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany.
Institute for Molecular Biosciences, Goethe University Frankfurt am Main, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany; Buchman Institute for Molecular Life Sciences, Goethe University Frankfurt am Main, Max-von-Laue Str. 15, D-60438 Frankfurt, Germany; Frankfurt Institute of Advanced Studies, Ruth-Moufang-Straße 1, D-60438 Frankfurt, Germany.
Biochim Biophys Acta Mol Cell Res. 2019 Apr;1866(4):663-672. doi: 10.1016/j.bbamcr.2019.01.004. Epub 2019 Jan 8.
The proteome of the outer membrane of mitochondria and chloroplasts consists of membrane proteins anchored by α-helical or β-sheet elements. While proteins with α-helical transmembrane domains are present in all cellular membranes, proteins with β-barrel structure are specific for these two membranes. The organellar β-barrel proteins are encoded in the nuclear genome and thus, have to be targeted to the outer organellar membrane where they are recognized by surface exposed translocation complexes. In the last years, the signals that ensure proper targeting of these proteins have been investigated as essential base for an understanding of the regulation of cellular protein distribution. However, the organellar β-barrel proteins are unique as most of them do not contain a typical targeting information in form of an N-terminal cleavable targeting signal. Recently, it was discovered that targeting and surface recognition of mitochondrial β-barrel proteins in yeast, humans and plants depends on the hydrophobicity of the last β-hairpin of the β-barrel. However, we demonstrate that the hydrophobicity is not sufficient for the discrimination of targeting to chloroplasts or mitochondria. By domain swapping between mitochondrial and chloroplast targeted β-barrel proteins atVDAC1 and psOEP24 we demonstrate that the presence of a hydrophilic amino acid at the C-terminus of the penultimate β-strand is required for mitochondrial targeting. A mutation of the chloroplast β-barrel protein psOEP24 which mimics such profile is efficiently targeted to mitochondria. Thus, we present the properties of the signal for mitochondrial targeting of β-barrel proteins in plants.
线粒体和叶绿体的外膜蛋白质组由通过 α-螺旋或 β-折叠元件锚定的膜蛋白组成。虽然具有 α-螺旋跨膜结构域的蛋白质存在于所有细胞膜中，但具有 β-桶结构的蛋白质是这两种膜的特异性。这些细胞器的β-桶蛋白是由核基因组编码的，因此必须靶向到外细胞器膜，在那里它们被表面暴露的转运复合物识别。在过去的几年中，已经研究了确保这些蛋白质正确靶向的信号，作为理解细胞蛋白质分布调节的基本基础。然而，这些细胞器的β-桶蛋白是独特的，因为它们中的大多数不包含典型的靶向信息，即 N 端可切割的靶向信号。最近发现，酵母、人类和植物中线粒体 β-桶蛋白的靶向和表面识别依赖于 β-桶最后一个 β-发夹的疏水性。然而，我们证明疏水性不足以区分靶向叶绿体或线粒体。通过在 VDAC1 和 psOEP24 之间进行线粒体和叶绿体靶向的 β-桶蛋白的结构域交换，我们证明在倒数第二个 β-链的 C 末端存在亲水性氨基酸是线粒体靶向所必需的。模拟这种特征的叶绿体 β-桶蛋白 psOEP24 的突变体能够有效地靶向线粒体。因此，我们提出了植物中β-桶蛋白线粒体靶向信号的特性。
