The biosynthesis of the alpha,beta-epoxyketone pharmacophore in natural product proteasome inhibitors

在过去的十年中，蛋白酶体已经发展成为一个有效的治疗靶点。2012年7月，Carfilzaldehyde（Kyprolis®），一种四肽环氧酮，在美国被批准用于复发性和难治性多发性骨髓瘤患者。它是从天然产物环氧霉素开发的，包含两个彼此紧邻的强亲电基团的独特药效团：α，β-环氧酮弹头。该结构基团允许与真核蛋白酶体的胰凝乳蛋白酶样部分高度特异性和不可逆结合。直到最近，人们对α，β-环氧酮的生物合成一无所知。在我们的初步工作中，我们确定和异源表达的epoxomicin和eponemycin基因簇。值得注意的是，α，β-环氧酮弹头的形成不能从基因簇中推断出来。因此，我们预测，不寻常的生物转化发生在终端聚酮化合物的转换。在这个项目中，我们打算阐明的生物合成途径，导致α，β-环氧酮。为此，我们将主要集中在异源基因缺失突变体的分析。我们还计划进行同位素富集前体进料实验。此外，将使用体外生物化学和蛋白质晶体学研究各个酶的催化机制。除此之外，基因组挖掘揭示了一个同源途径，我们假设该途径指导matlystatin样蛋白体抑制剂的形成。为了验证这一发现，我们将分离并异源表达相应的基因簇。这项实验应该作为我们未来基因组指导药物发现活动的概念证明。这项研究提案将使我们深入了解具有治疗意义的环氧酮类的生物学和生物起源，并将促进产生具有改进性能的蛋白酶体抑制剂。

The proteasome has advanced as a validated therapeutic target over the last decade. In July 2012 Carfilzomib (Kyprolis®) a tetrapeptide epoxyketone was approved for the use in patients with relapsed and refractory multiple myeloma in the USA. It was developed from the natural product epoxomicin comprising a unique pharmacophore of two strongly electrophilic groups in the immediate proximity to each other: the alpha,beta-epoxyketone warhead. This structural group allows a highly specific and irreversible binding to the chymotrypsin-like moiety of the eukaryotic proteasome. Until recently nothing was known about the biosynthesis of the alpha,beta-epoxyketone. In our preliminary work, we identified and heterologously expressed the epoxomicin and the eponemycin gene clusters. Notably, the formation of the alpha,beta-epoxyketone warhead could not be deduced from the gene clusters. We therefore predict that unusual biotransformations take place in the conversion of the terminal polyketide. In this project we intend elucidate the biosynthetic pathway which leads to the alpha,beta-epoxyketone. To this end we will primarily focus on the analysis of heterologous gene deletion mutants. We also plan to perform isotope-enriched precursor feeding experiments. Moreover, the catalytic mechanisms of respective enzymes will be investigated using in vitro biochemistry and protein crystallography. In addition to that, genome mining revealed a homologous pathway which we assume to direct the formation of matlystatin-like protesome inhibitors. To verify this finding, we will isolate and heterologously express the corresponding gene cluster. This experiment should serve as a proof of concept for our future genome-guided drug discovery campaigns. This research proposal will give us deep insides in the biology and biogenesis of the therapeutically important class of epoxyketones and will facilitate the generation of proteasome inhibitors with improved properties.