戊丙酯菌素生物合成基因簇中两个单加氧酶基因功能的研究

Streptomyces, antibiotic producers, is the largest genus of Actinobacteria which biosynthesizes abundant secondary metabolites including terpenoid compounds, for example, pentalenolactone. Pentalenolactone isolated from more than 30 species of Streptomyces is a widely occurring sesquiterpenoid antibiotic active against bacteria, fungi, protozoa and some DNA viruses，by reaction of the electrophilic epoxylactone moiety with the active-site cysteine of glyceraldehyde-3-phosphate dehydrogenase of glycolytic enzymes. There are five homologous gene clusters invovled in pentalenolactone biosynthesis, We will focus on P450 monooxygenase genes ptlI/pntI/penI and Baeyer-Villiger monooxygenase (BVMO) genes ptlE/pntE/penE to perfect pentalenolactone biosynthetic mechanism. Three homologous enzymes PtlI, PntI and PenI might be resposible for three-step oxidation of a methyl group to a carboxylic acid. This point need be proved by using genetics experiments and biochemistry experiments. Three homologous BVMO PtlE, PntE and PenE catalyze cyclic ketone to lactone, however, there are different regioselectivities between PtlE and PntE/PenE. We will find out amino acids that detemine the different regioselectivities by using site directed mutagensis.

链霉菌是抗生素的重要产生菌，有丰富的次生代谢产物，包括结构复杂多变的萜类物质，戊丙酯菌素(PL)就是其中的一种。PL是一种倍半萜类抗生素，具有抑制细菌、真菌、原生动物和DNA病毒的活性，作用于糖酵解途径中3-磷酸甘油醛脱氢酶活性中心的半胱氨酸。目前我们已发现有5簇与PL合成相关的同源基因簇，本项目从基因簇中细胞色素P450单加氧酶基因ptlI/penI/pntI和Baeyer-Villiger单加氧酶(BVMO)基因ptlE/penE/pntE入手，确定其功能，完善PL合成机制。同源基因ptlI、penI和pntI所编码的蛋白可能催化甲基生成羧基，需要遗传学和生化的实验数据来证明。同源基因ptlE、penE和pntE所编码的蛋白催化环酮生成内酯，但是PtlE与后两个蛋白表现出明显不同的区域选择性，我们将通过点突变来确定造成这种区域选择性差异的关键因素。

戊丙酯菌素是30多种链霉菌产生的一种倍半萜类抗生素，具有抑制细菌、真菌、原生动物、DNA病毒的生物学活性。 作用于细胞糖酵解途径中3-磷酸甘油醛脱氢酶活性中心的半胱氨酸。我们将从基因簇中细胞色素P450单加氧酶基因ptlI/pntI/penI和Baeyer-Villiger单加氧酶基因ptlE/pntE/penE入手，完善戊丙酯菌素的生物合成机制。我们的体内数据证明同源基因ptlI、pntI和penI所编码的蛋白能够催化甲基氧化生成羧基。同源基因ptlE、pntE和penE所编码的蛋白可以催化环酮生成内酯，但是PtlE与后两个蛋白表现出明显不同的区域选择性，我们通过突变关键的氨基酸来确定造成这种区域选择性差异的原因。