Pusnik Mascha, Charrière Fabien, Mäser Pascal, Waller Ross F, Dagley Michael J, Lithgow Trevor, Schneider André
Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland.
Mol Biol Evol. 2009 Mar;26(3):671-80. doi: 10.1093/molbev/msn288. Epub 2008 Dec 17.
All mitochondria have integral outer membrane proteins with beta-barrel structures including the conserved metabolite transporter VDAC (voltage dependent anion channel) and the conserved protein import channel Tom40. Bioinformatic searches of the Trypanosoma brucei genome for either VDAC or Tom40 identified a single open reading frame, with sequence analysis suggesting that VDACs and Tom40s are ancestrally related and should be grouped into the same protein family: the mitochondrial porins. The single T. brucei mitochondrial porin is essential only under growth conditions that depend on oxidative phosphorylation. Mitochondria isolated from homozygous knockout cells did not produce adenosine-triphosphate (ATP) in response to added substrates, but ATP production was restored by physical disruption of the outer membrane. These results demonstrate that the mitochondrial porin identified in T. brucei is the main metabolite channel in the outer membrane and therefore the functional orthologue of VDAC. No distinct Tom40 was identified in T. brucei. In addition to mitochondrial proteins, T. brucei imports all mitochondrial tRNAs from the cytosol. Isolated mitochondria from the VDAC knockout cells import tRNA as efficiently as wild-type. Thus, unlike the scenario in plants, VDAC is not required for mitochondrial tRNA import in T. brucei.
所有线粒体都有具有β-桶状结构的整合外膜蛋白，包括保守的代谢物转运体VDAC（电压依赖性阴离子通道）和保守的蛋白质导入通道Tom40。对布氏锥虫基因组进行生物信息学搜索以寻找VDAC或Tom40，结果鉴定出一个单一的开放阅读框，序列分析表明VDAC和Tom40在进化上相关，应归入同一蛋白家族：线粒体孔蛋白。布氏锥虫单一的线粒体孔蛋白仅在依赖氧化磷酸化的生长条件下才是必需的。从纯合敲除细胞中分离出的线粒体在添加底物时不产生三磷酸腺苷（ATP），但通过物理破坏外膜可恢复ATP的产生。这些结果表明，在布氏锥虫中鉴定出的线粒体孔蛋白是外膜中的主要代谢物通道，因此是VDAC的功能同源物。在布氏锥虫中未鉴定出独特的Tom40。除了线粒体蛋白外，布氏锥虫还从细胞质中导入所有线粒体tRNA。从VDAC敲除细胞中分离出的线粒体导入tRNA的效率与野生型一样高。因此，与植物中的情况不同，布氏锥虫线粒体tRNA的导入不需要VDAC。
