Thioesterase-like role for fungal PKS-NRPS hybrid reductive domains
Thioesterase-like role for fungal PKS-NRPS hybrid reductive domains
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DOI：
10.1021/ja803078z
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发表时间：
2008-08-20
影响因子：
15
通讯作者：
Schmidt, Eric W.
中科院分区：
文献类型：
--
作者：
Sims, James W.;Schmidt, Eric W.
尽管真菌还原聚酮化合物是由非常相似的酶合成的，但它们具有不同的结构，探索了广阔的化学空间领域。许多真菌聚酮化合物被多种氨基酸衍生的五元环、特特拉姆酸和相关的吡咯烷-2-酮封端。真菌中已知的特特拉姆酸合成酶含有 C 末端还原 (R) 结构域，这些结构域被认为在生成特特拉姆酸的过程中释放还原的吡咯烷-2-酮中间体。为了确定吡咯烷-2-一多样性的酶学基础，我们过表达木贼素合成酶 (EqiS) R 结构域，并分析了它们与合成底物类似物的反应性。我们表明 EqiS R 结构域不执行还原功能并且不结合还原辅因子。相反，EqiS R 催化 Dieckmann 缩合，估计 k(at) 接近 15 s(-1)。该作用不同于通常由短链脱氢酶/还原酶超家族酶催化的氧化还原反应。
Fungal reduced polyketides possess diverse structures exploring a broad region of chemical space despite their synthesis by very similar enzymes. Many fungal polyketides are capped by diverse amino acid-derived five-membered rings, the tetramic acids and related pyrrolidine-2-ones. The known tetramic acid synthetase enzymes in fungi contain C-terminal reductive (R) domains that were proposed to release reduced pyrrolidine-2-one intermediates en route to the tetramic acids. To determine the enzymatic basis of pyrrolidine-2-one diversity, we overexpressed equisetin synthetase (EqiS) R domains and analyzed their reactivity with synthetic substrate analogs. We show that the EqiS R domain does not perform a reducing function and does not bind reducing cofactors. Instead, the EqiS R catalyzes a Dieckmann condensation, with an estimated k(at) approximate to 15 s(-1). This role differs from the redox reactions normally catalyzed by short chain dehydrogenase/reductase superfamily enzymes.