Nekrutenko A, Hillis D M, Patton J C, Bradley R D, Baker R J
Department of Biological Sciences, Texas Tech University, Lubbock 79409, USA.
Mol Biol Evol. 1998 Dec;15(12):1674-84. doi: 10.1093/oxfordjournals.molbev.a025894.
In this study, we report cDNA sequences of the cytosolic NADP-dependent isocitrate dehydrogenase for humans, mice, and two species of voles (Microtus mexicanus and Microtus ochrogaster). Inferred amino acid sequences from these taxa display a high level of amino acid sequence conservation, comparable to that of myosin beta heavy chain, and share known structural features. A Caenorhabditis elegans enzyme that was previously identified as a protein similar to isocitrate dehydrogenase is most likely the NADP-dependent cytosolic isocitrate dehydrogenase enzyme equivalent, based on amino acid similarity to mammalian enzymes and phylogenetic analysis. We also suggest that NADP-dependent isocitrate dehydrogenases characterized from alfalfa, soybean, and eucalyptus are most likely cytosolic enzymes. The phylogenetic tree of various isocitrate dehydrogenases from eukaryotic sources revealed that independent gene duplications may have given rise to the cytosolic and mitochondrial forms of NADP-dependent isocitrate dehydrogenase in animals and fungi. There appears to be no statistical support for a hypothesis that the mitochondrial and cytosolic forms of the enzyme are orthologous in these groups. A possible scenario of the evolution of NADP-dependent isocitrate dehydrogenases is proposed.
在本研究中，我们报告了人类、小鼠以及两种田鼠（墨西哥田鼠和赭腹田鼠）的胞质NADP依赖性异柠檬酸脱氢酶的cDNA序列。从这些分类单元推断出的氨基酸序列显示出高度的氨基酸序列保守性，与肌球蛋白β重链相当，并具有已知的结构特征。基于与哺乳动物酶的氨基酸相似性和系统发育分析，先前被鉴定为与异柠檬酸脱氢酶相似的蛋白质的秀丽隐杆线虫酶很可能是等效的NADP依赖性胞质异柠檬酸脱氢酶。我们还认为，从苜蓿、大豆和桉树中鉴定出的NADP依赖性异柠檬酸脱氢酶很可能是胞质酶。真核生物来源的各种异柠檬酸脱氢酶的系统发育树表明，独立的基因复制可能导致了动物和真菌中NADP依赖性异柠檬酸脱氢酶的胞质和线粒体形式的产生。对于该酶的线粒体和胞质形式在这些群体中是直系同源的假设，似乎没有统计学支持。本文提出了NADP依赖性异柠檬酸脱氢酶进化的一种可能情况。
