Abstract
Background
Fungal polyketides include commercially important pharmaceuticals and food additives, e.g. the cholesterol-lowering statins and the red and orange monascus pigments. Presently, production relies on isolation of the compounds from the natural producers, and systems for heterologous production in easily fermentable and genetically engineerable organisms, such as Saccharomyces cerevisiae and Escherichia coli are desirable. Rubrofusarin is an orange polyketide pigment that is a common intermediate in many different fungal biosynthetic pathways.
Results
In this study, we established a biosynthetic pathway for rubrofusarin in S. cerevisiae. First, the Fusarium graminearum gene encoding polyketide synthase 12 (PKS12) was heterologously co-expressed with the Aspergillus fumigatus gene encoding phosphopantetheinyl transferase (npgA) resulting in production of YWA1. This aromatic heptaketide intermediate was converted into nor-rubrofusarin upon expression of the dehydratase gene aurZ from the aurofusarin gene cluster of F. graminearum. Final conversion into rubrofusarin was achieved by expression of the O-methyltransferase encoding gene aurJ, also obtained from the aurofusarin gene cluster, resulting in a titer of 1.1 mg/L. Reduced levels of rubrofusarin were detected when expressing PKS12, npgA, and aurJ alone, presumably due to spontaneous conversion of YWA1 to nor-rubrofusarin. However, the co-expression of aurZ resulted in an approx. six-fold increase in rubrofusarin production.
Conclusions
The reconstructed pathway for rubrofusarin in S. cerevisiae allows the production of a core scaffold molecule with a branch-point role in several fungal polyketide pathways, thus paving the way for production of further natural pigments and bioactive molecules. Furthermore, the reconstruction verifies the suggested pathway, and as such, it is the first example of utilizing a synthetic biological “bottom up” approach for the validation of a complex fungal polyketide pathway.
摘要
背景
真菌聚酮包括商业上重要的药物和食品添加剂,例如降低胆固醇的他汀类药物和红色和橙色的红曲霉素色素。目前,生产依赖于从天然生产者中分离化合物,并且希望在易于发酵和基因工程的生物体,例如酿酒酵母和大肠杆菌中进行异源生产系统。红曲霉素是一种橙色聚酮色素,是许多不同真菌生物合成途径中的常见中间体。
结果
在本研究中,我们在酿酒酵母中建立了红曲霉素的生物合成途径。首先,异源共表达了聚酮合成酶12(PKS12)基因和磷酸泛酰转移酶(npgA)基因,产生了YWA1。通过表达来自小麦镰刀菌aurofusarin基因簇的脱水酶基因aurZ,将这种芳香族七酮中间体转化为nor-rubrofusarin。通过表达O-甲基转移酶编码基因aurJ(也来自aurofusarin基因簇),最终转化为红曲霉素,产量为1.1mg/L。当单独表达PKS12,npgA和aurJ时,检测到红曲霉素的产量降低,可能是由于YWA1自发转化为nor-rubrofusarin。然而,共表达aurZ导致红曲霉素产量增加了约6倍。
结论
在酿酒酵母中重建红曲霉素的途径,可以生产具有在几种真菌聚酮途径中具有分支点作用的核心支架分子,从而为进一步的天然色素和生物活性分子的生产铺平道路。此外,重建验证了建议的途径,因此,这是利用合成生物学“自下而上”方法验证复杂真菌聚酮途径的第一个例子。