Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany.
Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
Elife. 2017 Aug 31;6:e28324. doi: 10.7554/eLife.28324.
Virtually all mitochondrial matrix proteins and a considerable number of inner membrane proteins carry a positively charged, N-terminal presequence and are imported by the TIM23 complex (presequence translocase) located in the inner mitochondrial membrane. The voltage-regulated Tim23 channel constitutes the actual protein-import pore wide enough to allow the passage of polypeptides with a secondary structure. In this study, we identify amino acids important for the cation selectivity of Tim23. Structure based mutants show that selectivity is provided by highly conserved, pore-lining amino acids. Mutations of these amino acid residues lead to reduced selectivity properties, reduced protein import capacity and they render the Tim23 channel insensitive to substrates. We thus show that the cation selectivity of the Tim23 channel is a key feature for substrate recognition and efficient protein import.
几乎所有的线粒体基质蛋白和相当数量的内膜蛋白都带有带正电荷的 N 端前导序列，并通过位于线粒体内膜的 TIM23 复合物（前导序列转位酶）进行输入。电压调节的 Tim23 通道构成了实际的蛋白质导入孔，其宽度足以允许具有二级结构的多肽通过。在这项研究中，我们确定了对 Tim23 阳离子选择性很重要的氨基酸。基于结构的突变体表明，选择性由高度保守的、位于孔内的氨基酸提供。这些氨基酸残基的突变导致选择性特性降低、蛋白质导入能力降低，并且使 Tim23 通道对底物不敏感。因此，我们表明，Tim23 通道的阳离子选择性是底物识别和有效蛋白质导入的关键特征。
