Smeitink Jan A M, Elpeleg Orly, Antonicka Hana, Diepstra Heleen, Saada Ann, Smits Paulien, Sasarman Florin, Vriend Gert, Jacob-Hirsch Jasmine, Shaag Avraham, Rechavi Gideon, Welling Brigitte, Horst Jurgen, Rodenburg Richard J, van den Heuvel Bert, Shoubridge Eric A
Nijmegen Centre for Mitochondrial Disorders, Department of Pediatrics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Am J Hum Genet. 2006 Nov;79(5):869-77. doi: 10.1086/508434. Epub 2006 Sep 15.
The 13 polypeptides encoded in mitochondrial DNA (mtDNA) are synthesized in the mitochondrial matrix on a dedicated protein-translation apparatus that resembles that found in prokaryotes. Here, we have investigated the genetic basis for a mitochondrial protein-synthesis defect associated with a combined oxidative phosphorylation enzyme deficiency in two patients, one of whom presented with encephalomyopathy and the other with hypertrophic cardiomyopathy. Sequencing of candidate genes revealed the same homozygous mutation (C997T) in both patients in TSFM, a gene coding for the mitochondrial translation elongation factor EFTs. EFTs functions as a guanine nucleotide exchange factor for EFTu, another translation elongation factor that brings aminoacylated transfer RNAs to the ribosomal A site as a ternary complex with guanosine triphosphate. The mutation predicts an Arg333Trp substitution at an evolutionarily conserved site in a subdomain of EFTs that interacts with EFTu. Molecular modeling showed that the substitution disrupts local subdomain structure and the dimerization interface. The steady-state levels of EFTs and EFTu in patient fibroblasts were reduced by 75% and 60%, respectively, and the amounts of assembled complexes I, IV, and V were reduced by 35%-91% compared with the amounts in controls. These phenotypes and the translation defect were rescued by retroviral expression of either EFTs or EFTu. These data clearly establish mutant EFTs as the cause of disease in these patients. The fact that the same mutation is associated with distinct clinical phenotypes suggests the presence of genetic modifiers of the mitochondrial translation apparatus.
线粒体DNA（mtDNA）编码的13种多肽是在类似于原核生物的专用蛋白质翻译装置上于线粒体基质中合成的。在此，我们研究了两名患者线粒体蛋白质合成缺陷的遗传基础，该缺陷与氧化磷酸化酶联合缺乏有关，其中一名患者患有脑肌病，另一名患有肥厚性心肌病。对候选基因进行测序发现，两名患者的TSFM基因均存在相同的纯合突变（C997T），TSFM基因编码线粒体翻译延伸因子EFTs。EFTs作为EFTu的鸟嘌呤核苷酸交换因子发挥作用，EFTu是另一种翻译延伸因子，它将氨酰化转运RNA作为与三磷酸鸟苷的三元复合物带到核糖体A位点。该突变预测在EFTs与EFTu相互作用的亚结构域中一个进化保守位点发生Arg333Trp替换。分子建模显示，该替换破坏了局部亚结构域结构和二聚化界面。与对照组相比，患者成纤维细胞中EFTs和EFTu的稳态水平分别降低了75%和60%，组装的复合物I、IV和V的量减少了35% - 91%。通过逆转录病毒表达EFTs或EFTu可挽救这些表型和翻译缺陷。这些数据明确确定突变的EFTs是这些患者的病因。同一突变与不同临床表型相关这一事实表明存在线粒体翻译装置的遗传修饰因子。
