ABSTRACT
Sesquiterpene synthases are responsible for the cyclization of farnesyl pyrophosphate into a myriad of structurally diverse compounds with various biological activities. We examine here the role of the conserved active site H-α1 loop in catalysis in three previously characterized fungal sesquiterpene synthases. The H-α1 loops of Cop3, Cop4, and Cop6 from
Coprinus cinereus
were altered by site-directed mutagenesis and the resultant product profiles were analyzed by gas chromatography-mass spectrometry and compared to the wild-type enzymes. In addition, we examine the effect of swapping the H-α1 loop from the promiscuous enzyme Cop4 with the more selective Cop6 and the effect of acidic or basic conditions on loop mutations in Cop4. Directed mutations of the H-α1 loop had a marked effect on the product profile of Cop3 and Cop4, while little to no change was shown in Cop6. Swapping of the Cop4 and Cop6 loops with one another was again shown to influence the product profile of Cop4, while the product profile of Cop6 remained identical to the wild-type enzyme. The loop mutations in Cop4 also implicate specific residues responsible for the pH sensitivity of the enzyme. These results affirm the role of the H-α1 loop in catalysis and provide a potential target to increase the product diversity of terpene synthases.
摘要
倍半萜合酶负责将焦磷酸法呢基环化成具有各种生物活性的结构多样的化合物。我们在此研究了保守的活性位点 H-α1 环在三个先前表征的真菌倍半萜合成酶催化作用中的作用。Cop3、Cop4 和 Cop6 的 H-α1 环来自于
Coprinus cinereus
通过定点突变改变了这些酶的 H-α1 环,并用气相色谱-质谱法分析了所得到的产物图谱,并将其与野生型酶进行了比较。此外,我们还研究了将杂合酶 Cop4 的 H-α1 环与选择性更强的 Cop6 互换的效果,以及酸性或碱性条件对 Cop4 环突变的影响。H-α1 环的定向突变对 Cop3 和 Cop4 的产物特征有明显影响,而 Cop6 几乎没有变化。Cop4 和 Cop6 环路的相互交换再次证明会影响 Cop4 的产物特征,而 Cop6 的产物特征则与野生型酶保持一致。Cop4 的环突变还牵涉到负责该酶 pH 敏感性的特定残基。这些结果肯定了 H-α1 环在催化中的作用,并为增加萜烯合成酶的产物多样性提供了一个潜在的目标。