Hu C A, Delauney A J, Verma D P
Department of Molecular Genetics, Ohio State University, Columbus 43210-1002.
Proc Natl Acad Sci U S A. 1992 Oct 1;89(19):9354-8. doi: 10.1073/pnas.89.19.9354.
Many plants synthesize and accumulate proline in response to osmotic stress. Despite the importance of this pathway, however, the exact metabolic route and enzymes involved in the synthesis of proline in plants have not been unequivocally identified. We report here the isolation of a mothbean (Vigna aconitifolia) cDNA clone encoding a bifunctional enzyme, delta 1-pyrroline-5-carboxylate synthetase (P5CS), with both gamma-glutamyl kinase and glutamic-gamma-semialdehyde dehydrogenase activities that catalyzes the first two steps in proline biosynthesis. The two enzymatic domains of P5CS correspond to the ProB and ProA proteins of Escherichia coli and contain a leucine zipper in each domain, which may facilitate inter- or intramolecular interaction of this protein. The Vigna P5CS enzyme activity is feedback regulated by proline but is less sensitive to end-product inhibition than is the E. coli gamma-glutamyl kinase. The P5CS gene is expressed at high levels in Vigna leaves and is inducible in roots subjected to salt stress, suggesting that P5CS plays a key role in proline biosynthesis, leading to osmoregulation in plants.
许多植物在渗透胁迫下会合成并积累脯氨酸。然而，尽管这条途径很重要，但植物中脯氨酸合成的确切代谢途径和相关酶尚未得到明确鉴定。我们在此报告了从蛾豆（Vigna aconitifolia）中分离出一个cDNA克隆，该克隆编码一种双功能酶，即δ1-吡咯啉-5-羧酸合成酶（P5CS），它具有γ-谷氨酰激酶和谷氨酰-γ-半醛脱氢酶活性，催化脯氨酸生物合成的前两个步骤。P5CS的两个酶结构域分别对应于大肠杆菌的ProB和ProA蛋白，并且每个结构域都含有一个亮氨酸拉链，这可能有助于该蛋白的分子间或分子内相互作用。蛾豆P5CS酶活性受脯氨酸的反馈调节，但比大肠杆菌γ-谷氨酰激酶对终产物抑制的敏感性更低。P5CS基因在蛾豆叶片中高水平表达，并且在遭受盐胁迫的根中可诱导表达，这表明P5CS在脯氨酸生物合成中起关键作用，从而导致植物中的渗透调节。
