The plant aspartate aminotransferase gene family
The plant aspartate aminotransferase gene family
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DOI：
10.1111/j.1399-3054.1997.tb00028.x
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发表时间：
1997-08
影响因子：
6.4
通讯作者：
G. J. Wadsworth
中科院分区：
文献类型：
--
作者：
G. J. Wadsworth
在植物中，天冬氨酸转氨酶作为多种同工酶存在。这些AAT同工酶至少在四个不同的亚细胞区室中有不同的定位，包括细胞质、质体、线粒体和过氧化物酶体。最近对几种植物AAT编码的cDNA和基因组序列的鉴定，为AAT同工酶的结构、亚细胞靶向和进化提供了深入的了解。AAT同工酶似乎通过与其他靶向蛋白相同的机制靶向亚细胞区室。质体AAT和线粒体AAT都是作为具有适当n端靶向序列的前体合成的，这些序列在各自的细胞器中定位后被蛋白水解去除。胞质AAT同工酶缺乏明显的靶向序列，因此限制了其在胞质中的作用。过氧化物酶体AAT尚未克隆，因此尚未对其靶向性进行研究。序列分析表明，植物AAT同工酶与脊椎动物和细菌AAT同工酶属于同一蛋白家族。此外，脊椎动物和植物线粒体AAT同工酶的相似性表明，这种AAT同工酶的进化可能早于植物和动物的分化。对质体和细胞质AAT的分析表明，它们比线粒体基因分化得更晚。序列分析还显示细胞质AAT的分化速度是质体AAT的1.6倍。利用cDNA和基因组克隆对豆科植物结瘤过程中AAT基因的表达进行了研究，结果表明，AAT在豆科植物结瘤过程中的表达受转录水平的控制。
Aspartate aminotransferase exists as multiple isozymes in plants. These AAT isozymes are differentially localized in at least four different subcellular compartments, including the cytosol, plastids, mitochondria, and peroxisomes. The recent characterization of cDNA and genomic sequences encoding AAT from several plants has provided insight into the structure, subcellular targeting, and evolution of the AAT isozymes. The AAT isozymes appear to be targeted to subcellular compartments by the same mechanisms utilized by other targeted proteins. Both the plastid AAT and mitochondrial AAT are synthesized as precursors with appropriate N-terminal targeting sequences which are proteolytically removed after localization in their respective organelles. The cytosolic AAT isozymes lack apparent targeting sequences, thus restricting it to the cytosol. A peroxisomal AAT has not been cloned and therefore its targeting has not been investigated. Sequence analysis demonstrates that the plant AAT isozymes are in the same protein family as the vertebrate and bacterial AATs. Furthermore, similarity between vertebrate and plant mitochondrial AAT isozymes suggest the evolution of this AAT isozyme may predate the divergence of plants and animals. Analysis of plastid and cytosolic AAT suggests that they have diverged more recently than the mitochondrial gene. The sequence analysis also reveals that the cytosolic AAT is diverging at a rate 1.6 times faster than the plastid AAT. The cDNA and genomic clones have been used to investigate expression of the AAT genes during nodulation in legumes and suggest that the nodule-enhanced expression of plastid AAT is controlled at the transcriptional level.