表面活性素（surfactin）是由枯草芽孢杆菌非核糖体肽合成酶（NRPS）合成的典型脂肽（lipopeptides）化合物，除具有优异的表面活性外，还具有抗菌、抑癌和抗病毒等生物学活性，但surfactin的溶血活性阻碍了进一步应用。surfactin烷基脂酰结构不但对其理化性质和生物学活性有显著的影响，还是surfactin合成的起始底物。本项目研究枯草芽孢杆菌surfactin合成酶srfAA的合成起始模块（C-AGlu-PCP）对脂酰结构前体（中长链R-3羟基脂酰CoA）的底物选择性，基于组合生物合成技术提升srfAA起始模块的合成能力，解析脂肪酸代谢途径对脂酰结构前体的合成和调控机制，重构脂肪酸β-氧化途径定向合成脂酰基结构前体，获得特定脂酰结构的surfactin新分子。定向合成surfactin烷基脂酰结构的设计理念和技术平台，对于开发脂肽类新结构化合物具有重要的示范意义。

The cyclic lipopeptides, assembled by nonribosomal peptide synthetases (NRPSs) as secondary metabolites in microorganisms, are a new class of antibiotics. They are also characterized by having a medium to long fatty acyl chain attached to the macrocyclic peptide core. Structural activity relationship (SAR) studies have shown that variations in the lipid side chains of lipopeptide have significant affects on their bioactivity and properties. Surfactin, a cyclic lipoheptapeptide lactone produced by Bacillus subtilis, contains seven amino acid residues and one 3-hydroxy fatty acid. Besides its excellent properties as a biosurfactant, surfactin also exhibits antibacterial, -viral, -tumoral, and antimycoplasmatic activities, which make it an interesting target for therapeutic applications. Only its cytotoxicity against erythrocytes, which is greatly affected by the fatty acid moieties, prevents surfactin from clinical applications. The fatty acyl chains of surfactin are also the first substructure incorporated into the peptidyl backbone via a process known as lipoinitiation. Therefore, understanding the pathways of fatty acyl precursor for surfactin synthesis is of special interest as it might facilitate the design of new products with improved properties. In this proposal, we want to investigate and modify the lipid chains of surfactins, the detailed work including: (1) investigating the dissected initiation module (C-AGlu-PCP) of surfactin synthetase SrfAA in vitro to gain its substrate specificity for medium to long chain of CoA-activated 3-hydroxy fatty acids; (2) identifying the enzymes for 3-hydroxy-fatty acids(or CoA-activated 3-hydroxy fatty acids) from fatty acid de nove biosynthesis pathway or beta-oxidation pathway; (3) constructing pathways for directed biosynthesis of CoA-activated 3-hydroxy fatty acids by feeding fatty acids as precursor and subsequently incorporated into the peptidyl backbone via lipoinitiation process to form designed surfactin new products.