Arabidopsis thaliana defense-related protein ELI3 is an aromatic alcohol:NADP(+) oxidoreductase

We expressed a cDNA encoding the Arabidopsis thaliana defense-related protein ELI3-2 in Escherichia coli to determine its biochemical function. Based on a protein database search, this protein was recently predicted to be a mannitol dehydrogenase [Williamson, J. D., Stoop, J. M. H., Massel, M. O., Conkling, M. A. & Pharr, D. M. (1995) Proc. Natl. Acad. Sci. USA 92, 7148–7152]. Studies on the substrate specificity now revealed that ELI3-2 is an aromatic alcohol: NADP(+) oxidoreductase (benzyl alcohol dehydrogenase). The enzyme showed a strong preference for various aromatic aldehydes as opposed to the corresponding alcohols. Highest substrate affinities were observed for 2-methoxybenzaldehyde, 3-methoxybenzaldehyde, salicylaldehyde, and benzaldehyde, in this order, whereas mannitol dehydrogenase activity could not be detected. These and previous results support the notion that ELI3-2 has an important role in resistance-related aromatic acid-derived metabolism.

为明确拟南芥（Arabidopsis thaliana）防御相关蛋白ELI3-2的生化功能，我们将其编码的互补DNA（cDNA）在大肠杆菌（Escherichia coli）中进行了异源表达。此前基于蛋白质数据库检索，该蛋白曾被预测为甘露醇脱氢酶（mannitol dehydrogenase）[Williamson, J. D., Stoop, J. M. H., Massel, M. O., Conkling, M. A. & Pharr, D. M. (1995) Proc. Natl. Acad. Sci. USA 92, 7148–7152]。本研究通过底物特异性分析现已发现，ELI3-2实为芳香醇：NADP(+)氧化还原酶（苯甲醇脱氢酶（benzyl alcohol dehydrogenase））。该酶对多种芳香醛表现出极强的底物偏好性，而非对应的芳香醇。其对2-甲氧基苯甲醛、3-甲氧基苯甲醛、水杨醛及苯甲醛的底物亲和力依次最高，且未检测到甘露醇脱氢酶活性。上述结果结合既往研究均支持ELI3-2在抗性相关的芳香酸衍生代谢过程中发挥重要作用这一结论。