Houstĕk J, Klement P, Hermanská J, Houstková H, Hansíková H, Van den Bogert C, Zeman J
Institute of Physiology, Academy of Sciences of the Czech Republic, Prague.
Biochim Biophys Acta. 1995 Jun 9;1271(2-3):349-57. doi: 10.1016/0925-4439(95)00063-a.
A family is described with a T-->G mutation at position 8993 of mtDNA. This mutation is located in the ATPase 6 gene of mtDNA which encodes subunit a of the ATP-synthase complex (FlFo-ATPase). Clinically, the patients showed severe infantile lactate acidosis and encephalomyopathy in a form that was different from the classical Leigh syndrome. In 3 affected boys, ranging in age from 3 months to 8 years, the mutation was found in 95-99% of the mtDNA population. The clinical symptoms correlated with the mtDNA heteroplasmy and in the healthy mother 50% of the mtDNA was mutated. The rate of mitochondrial ATP production by cultured skin fibroblasts containing 99% of mutated mtDNA was about 2-fold lower than that in normal fibroblasts. Native electrophoresis of the mitochondrial enzyme complexes revealed instability of the FlFo-ATPase in all the tissues of the patient that were investigated (heart, muscle, kidney, liver). Only a small portion of the ATP-synthase complex was present in the complete, intact form (620 kDa). Incomplete forms of the enzyme were present as subcomplexes with approx. molecular weights of 460, 390 and 150 kDa, respectively, which differed in the content of F1 and Fo subunits. Immunochemical analysis of the subunits of the FlFo-ATPase further revealed a markedly decreased content of the Fo subunit b in mitochondria from muscle and heart, and an increased content of the Fo subunit c in muscle mitochondria, respectively. These results indicate that in this family the T-->G point mutation at position 8993 in the mitochondrial ATPase 6 gene is accompanied by structural instability and altered assembly of the enzyme complex, that are both most likely due to changes in the properties of subunit a of the membrane sector part of the ATP-synthase.
本文描述了一个家系，其线粒体DNA（mtDNA）第8993位发生了T→G突变。该突变位于mtDNA的ATP酶6基因，该基因编码ATP合酶复合物（FlFo - ATP酶）的a亚基。临床上，患者表现为严重的婴儿乳酸酸中毒和脑肌病，其形式不同于经典的Leigh综合征。在3名年龄从3个月到8岁的患病男孩中，该突变存在于95% - 99%的mtDNA群体中。临床症状与mtDNA异质性相关，在健康母亲中50%的mtDNA发生了突变。含有99%突变mtDNA的培养皮肤成纤维细胞的线粒体ATP产生率比正常成纤维细胞低约2倍。线粒体酶复合物的天然电泳显示，在所有被研究的患者组织（心脏、肌肉、肾脏、肝脏）中，FlFo - ATP酶不稳定。只有一小部分ATP合酶复合物以完整、未受损的形式（620 kDa）存在。酶的不完整形式以亚复合物形式存在，其分子量分别约为460、390和150 kDa，F1和Fo亚基的含量不同。对FlFo - ATP酶亚基的免疫化学分析进一步显示，肌肉和心脏线粒体中Fo亚基b的含量明显降低，而肌肉线粒体中Fo亚基c的含量增加。这些结果表明，在这个家系中，线粒体ATP酶6基因第8993位的T→G点突变伴随着酶复合物的结构不稳定和组装改变，这很可能都是由于ATP合酶膜区部分a亚基性质的改变所致。
