Designer phytoalexins: probing camalexin detoxification pathways in the phytopathogen Rhizoctonia solaniElectronic supplementary information (ESI) available: 1H and 13C NMR spectral data for camalexin (1). See http://www.rsc.org/suppdata/ob/b4/b400031e/
作者:M. Soledade C. Pedras、Jun Liu
DOI:10.1039/b400031e
日期:——
To probe the specificity of a camalexin detoxifying enzyme(s) produced by Rhizoctonia solani, the putative 5-camalexin hydroxylase (5-CAHY), the naturally occurring phytoalexin 1-methylcamalexin and designer phytoalexins in which the H-5 of camalexin was replaced with either a methyl group or a fluorine atom were synthesised. This investigation showed that biotransformation of 5-fluorocamalexin by R. solani was substantially slower than that of camalexin (12 days vs. six to eight hours), 5-methylcamalexin (5–6 days) or 1-methylcamalexin (5–6 days). Antifungal bioassays showed that 5-fluorocamalexin, 5-methylcamalexin and 1-methylcamalexin were more inhibitory to R. solani than camalexin, whereas their metabolic products displayed substantially lower inhibitory activity. It was concluded that detoxification via oxidation of the indole moiety of camalexins is predominant in the biotransformation of both camalexin and 5-methylcamalexin and likely catalysed by a specific 5-CAHY. By contrast, the pathways for detoxification of 1-methylcamalexin and 5-fluorocamalexin are likely catalysed by non-specific “house-keeping” enzymes. Most importantly, because 1- methylcamalexin showed stronger antifungal activity and was metabolised at substantially slower rate than camalexin this work suggested that, from a plant's perspective 1-methylcamalexin could be a more effective antifungal defence than camalexin.
为了探究根瘤菌产生的一种(多种)骆驼蓬苷解毒酶的特异性,合成了假定的 5-骆驼蓬苷羟化酶(5-CAHY)、天然存在的植物骆驼蓬苷 1-甲基骆驼蓬苷以及将骆驼蓬苷的 H-5 替换为甲基或氟原子的设计植物骆驼蓬苷。调查显示,茄属酵母菌对 5-氟氨骆驼祥霉素的生物转化速度大大慢于骆驼祥霉素(12 天对 6-8 小时)、5-甲基氨骆驼祥霉素(5-6 天)或 1-甲基氨骆驼祥霉素(5-6 天)。抗真菌生物测定结果表明,5-氟骆驼蓬苷、5-甲基骆驼蓬苷和 1-甲基骆驼蓬苷对 R. solani 的抑制作用比骆驼蓬苷更强,而其代谢产物的抑制活性则低得多。由此得出结论,在骆驼蓬苷和 5-甲基骆驼蓬苷的生物转化过程中,通过氧化骆驼蓬苷的吲哚分子进行解毒是最主要的途径,而且很可能是由特定的 5-CAHY 催化的。相比之下,1-甲基骆马毒素和 5-氟骆马毒素的解毒途径可能是由非特异性的 "看家 "酶催化的。最重要的是,由于 1-甲基骆驼蓬苷显示出更强的抗真菌活性,而且代谢速度大大慢于骆驼蓬苷,这项工作表明,从植物的角度来看,1-甲基骆驼蓬苷可能是一种比骆驼蓬苷更有效的抗真菌剂。