4-<i>O</i>-Acetylation and 3-<i>O</i>-Acetylation of Trichothecenes by Trichothecene 15-<i>O</i>-Acetyltransferase Encoded by<i>Fusarium Tri3</i>
作者:Takeshi TOKAI、Naoko TAKAHASHI-ANDO、Masumi IZAWA、Takashi KAMAKURA、Minoru YOSHIDA、Makoto FUJIMURA、Makoto KIMURA
DOI:10.1271/bbb.80501
日期:2008.9.23
In the biosynthesis of Fusarium trichothecenes, the C-3 hydroxyl group of isotrichodermol must be acetylated by TRI101 for subsequent pathway genes to function. Despite the importance of this 3-O-acetylation step in biosynthesis, Tri101 is both physically and evolutionarily unrelated to other Tri genes in the trichothecene gene cluster. To gain insight into the evolutionary history of the cluster, we purified recombinant TRI3 (rTRI3), one of the two cluster gene-encoded trichothecene O-acetyltransferases, and examined to determine whether this 15-O-acetyltransferase can add an acetyl to the C-3 hydroxyl group of isotrichodermol. When a high concentration of rTRI3 was used in the assay (final concentration, 50 μm), we observed 3-O-acetylation activity against isotrichodermol that was more than 105 times less efficient than the known 15-O-acetylation activity against 15-deacetylcalonectrin. The rTRI3 protein also exhibited 4-O-acetylation activity when nivalenol was used as a substrate; in addition to 15-acetylnivalenol, di-acetylated derivatives, 4,15-diacetylnivalenol, and, to a lesser extent, 3,15-diacetylnivalenol, were also detected at high enzyme concentrations. The significance of the trace trichothecene 3-O-acetyltransferase activity detected in rTRI3 is discussed in relation to the evolution of the trichothecene gene cluster.
在镰刀菌毒素的生物合成中,isotrichodermol 的 C-3 羟基必须通过 TRI101 乙酰化,以便后续通路基因发挥功能。尽管这一 3-O-乙酰化步骤在生物合成中至关重要,但 Tri101 在物理和进化上都与萎蔫酸基因簇中的其他 Tri 基因无关。为了深入了解该基因簇的进化历史,我们纯化了其中一种编码萎蔫酸 O-乙酰基转移酶的基因簇 TRI3(rTRI3),并检测了这种 15-O-乙酰基转移酶是否能将乙酰基添加到 isotrichodermol 的 C-3 羟基上。当在检测中使用高浓度的 rTRI3 时(最终浓度为 50 μM),我们观察到对 isotrichodermol 的 3-O-乙酰化活性,其效率比对 15-去乙酰甲虫素已知的 15-O-乙酰化活性低 105 倍以上。当以雪腐镰刀菌烯醇作为底物时,rTRI3 蛋白还表现出 4-O-乙酰化活性;除了 15-乙酰雪腐镰刀菌烯醇外,在高酶浓度下还检测到二乙酰化衍生物 4,15-二乙酰雪腐镰刀菌烯醇,以及较少程度的 3,15-二乙酰雪腐镰刀菌烯醇。本文讨论了在 rTRI3 中检测到的微量萎蔫酸 3-O-乙酰基转移酶活性与萎蔫酸基因簇进化之间的关系。