人参达玛烯二醇-Ⅱ合酶在酿酒酵母中的表达、定位及功能研究

Expression, subcellular localization and characterization of dammarenediol-Ⅱ synthase of Panax ginseng in Saccharomyces cerevisiae

为了研究人参达玛烯二醇-Ⅱ合酶(dammarenediol-Ⅱ synthase,DS)在酿酒酵母中的重组表达和定位,本研究克隆了人参中达玛烯二醇-Ⅱ合酶基因ds,并将其与绿色荧光蛋白基因gfp融合,构建了相应的重组表达质粒pESC-HIS-DS和pESC-HIS-DS-GFP,转化酿酒酵母INVSc1,获得了重组菌INVSc1-DS和INVSc1-DS-GFP。通过差速离心法制备重组菌微粒体,荧光显微镜下观察达玛烯二醇-Ⅱ合酶的表达及亚细胞定位,并通过酶促反应对该酶进行了功能鉴定,结果表明,DS为膜结合型蛋白,在体外能催化2,3-氧化鲨烯生成达玛烯二醇-Ⅱ。对重组菌发酵产物进行分析,结果表明,重组菌中产生了达玛烯二醇-Ⅱ,且通过将ds与gfp融合,重组菌中的达玛烯二醇-Ⅱ产量由7.53 mg·g^(-1)提高到12.24 mg·g^(-1),该结果为优化在酿酒酵母中构建的人参皂苷代谢途径提供了新思路。

To study the expression and subcellular localization of recombinant dammarenediol-Ⅱ synthase（DS） in Saccharomyces cerevisiae, the dammarenediol-Ⅱ synthase gene ds was cloned from Panax ginseng, and the gene ds was fused with the gene of green fluorescent protein to obtain the fusion gene ds-gfp. The recombinant expression plasmids pESC-HIS-DS and pESC-HIS-DS-GFP were constructed and transformed into S. cerevisiae INVSc1 to obtain recombinant strains INVSc1-DS and INVSc1-DS-GFP. Microsomes of recombinant strains were prepared by differential centrifugation and observed by fluorescence microscope. The green fluorescence was only detected in INVSc1-DS-GFP microsomes, which indicated that DS was a membrane protein. It was also proved that dammarenediol-Ⅱ was produced from the cyclization of 2,3-oxidosqualene catalyzed by DS through in vitro enzymatic reaction. In addition, our results revealed that the fusion expression of ds with gfp significantly improved the production of dammarenediol-Ⅱ from 7.53 mg·g^（-1） to 12.24 mg·g^（-1）. This study provides a new strategy in the optimization of the pathway of ginsenosides biosynthesis in S.cerevisiae.