Naghdi Shamim, Várnai Péter, Hajnóczky György
MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107;
Department of Physiology, Faculty of Medicine, Semmelweis University, Budapest 1094, Hungary.
Proc Natl Acad Sci U S A. 2015 Oct 13;112(41):E5590-9. doi: 10.1073/pnas.1510574112. Epub 2015 Sep 28.
Voltage-dependent anion channel (VDAC) proteins are major components of the outer mitochondrial membrane. VDAC has three isoforms with >70% sequence similarity and redundant roles in metabolite and ion transport. However, only Vdac2(-/-) (V2(-/-)) mice are embryonic lethal, indicating a unique and fundamental function of VDAC2 (V2). Recently, a specific V2 requirement was demonstrated for mitochondrial Bak import and truncated Bid (tBid)-induced apoptosis. To determine the relevant domain(s) of V2 involved, VDAC1 (V1) and V2 chimeric constructs were created and used to rescue V2(-/-) fibroblasts. Surprisingly, the commonly cited V2-specific N-terminal extension and cysteines were found to be dispensable for Bak import and high tBid sensitivity. In gain-of-function studies, V2 (123-179) was the minimal sequence sufficient to render V1 competent to support Bak insertion. Furthermore, in loss-of-function experiments, T168 and D170 were identified as critical residues. These motifs are conserved in zebrafish V2 (zfV2) that also rescued V2-deficient fibroblasts. Because high-resolution structures of zfV2 and mammalian V1 have become available, we could superimpose these structures and recognized that the critical V2-specific residues help to create a distinctive open "pocket" on the cytoplasmic surface that could facilitate Bak recruitment.
电压依赖性阴离子通道（VDAC）蛋白是线粒体外膜的主要成分。VDAC有三种亚型，序列相似度超过70%，在代谢物和离子转运中发挥冗余作用。然而，只有Vdac2基因敲除（V2基因敲除）小鼠在胚胎期致死，这表明VDAC2（V2）具有独特且基本的功能。最近，研究表明线粒体Bak导入和截短型Bid（tBid）诱导的凋亡需要特定的V2。为了确定V2中涉及的相关结构域，构建了VDAC1（V1）和V2嵌合构建体，并用于挽救V2基因敲除的成纤维细胞。令人惊讶的是，通常提到的V2特异性N端延伸和半胱氨酸对于Bak导入和高tBid敏感性是可有可无的。在功能获得性研究中，V2（123 - 179）是使V1能够支持Bak插入的最小序列。此外，在功能丧失性实验中，T168和D170被确定为关键残基。这些基序在斑马鱼V2（zfV2）中是保守的，zfV2也能挽救V2缺陷的成纤维细胞。由于zfV2和哺乳动物V1的高分辨率结构已经获得，我们可以叠加这些结构，并认识到关键的V2特异性残基有助于在细胞质表面形成一个独特的开放“口袋”，这可能有助于Bak的募集。
