AbstractThree central steps during the biosynthesis of cytochalasan precursors, including reductive release, Knoevenagel cyclisation and Diels Alder cyclisation are not yet understood at a detailed molecular level. In this work we investigated the reductive release step catalysed by a hybrid polyketide synthase non‐ribosomal peptide synthetase (PKS‐NRPS) from the pyrichalasin H pathway. Synthetic thiolesters were used as substrate mimics for in vitro studies with the isolated reduction (R) and holo‐thiolation (T) domains of the PKS‐NRPS hybrid PyiS. These assays demonstrate that the PyiS R‐domain mainly catalyses an NADPH‐dependent reductive release of an aldehyde intermediate that quickly undergoes spontaneous Knoevenagel cyclisation. The R‐domain can only process substrates that are covalently bound to the phosphopantetheine thiol of the upstream T‐domain, but it shows little selectivity for the polyketide.
摘要细胞分裂素前体生物合成过程中的三个核心步骤,包括还原释放、Knoevenagel 环化和 Diels Alder 环化,尚未在分子水平上得到详细了解。在这项工作中,我们研究了由吡咯烷酮 H 途径中的混合多酮合成酶非核糖体肽合成酶(PKS-NRPS)催化的还原释放步骤。合成硫醇酯被用作底物模拟物,与 PKS-NRPS 杂交 PyiS 的分离还原(R)和全硫化(T)结构域一起进行体外研究。这些检测结果表明,PyiS 的 R 结构域主要催化 NADPH 依赖性还原释放醛中间体,该中间体会迅速发生自发的 Knoevenagel 循环。R-domain 只能处理与上游 T-domain 的磷酸泛硫硫氨酸硫醇共价结合的底物,但对多酮类化合物几乎没有选择性。