Enzymes of the chalcone synthase superfamily from plants and microorganisms

植物次生代谢物如黄酮类(紫外线防护)、异黄酮类(根瘤菌结瘤)、花青素(花色)和抗菌植物防御素都是由查尔酮合成酶(CHS)超家族成员合成的聚酮类化合物。这些酶很小(约42 kDa亚基的同源二聚体)，但非常复杂，在单个活性部位催化多步反应。因此，它们为其他多组分聚酮合成酶提供了一个很好的模型，这些聚酮合成酶负责各种有用的天然产物的生物合成，包括抗生素、免疫抑制剂和抗癌剂。最近对CHS及其相关酶的结构和机理的研究已经对CHS超家族的酶机制和生物合成多功能性的分子基础有了深入的了解。二苯乙烯合酶是二苯乙烯超家族中的另一个代表性成员，由于其抗真菌活性和许多有益的健康效应，在转基因作物的开发中引起了极大的关注。利用尚未探索的生物有机化学方法对STS催化的环化反应进行的机理研究将提供迫切需要的见解，这些见解将被证明对通过代谢工程操纵聚酮生物合成有价值。对蓝藻、固氮菌、苔藓和原始植物马尾草的类CHS酶的研究已经在进行中。这些研究结果将有助于更好地了解植物和微生物中酶家族的进化和代谢途径。最后，花药特有CHSS的苔藓同源物可能会为了解植物雄性可育性的鲜为人知的过程提供洞察。

Plant secondary metabolites such as flavonoids (UV protection), isoflavonoids (Rhizobium nodulation), anthocyanins (floral color), and antimicrobial phytoalexins are all derived from polyketides synthesized by the members of chalcone synthase (CHS) superfamily. These enzymes are small (homodimer of ~42 kDa subunits), yet remarkably complex enzymes and catalyze multiple-step reactions at a single active site. Thus, they provide a good model for other multi-component polyketide synthases, which are responsible for biosynthesis of a variety of useful natural products including antibiotics, immunosuppressants and anticancer agents. Recent structural and mechanistic studies on CHS and related enzymes have yielded insights into enzyme mechanisms and the molecular basis of biosynthetic versatility of the CHS superfamily. Stilbene synthase, another representative member of the superfamily, has attracted much attention in transgenic crop development due to the antifungal activity and a number of beneficial health effects of stilbenes. The proposed mechanistic study on the STS-catalyzed cyclization reaction using unexplored bioorganic chemical approaches will provide much needed insight that should prove valuable in the manipulation of polyketide biosynthesis through metabolic engineering. Already underway are studies on CHS-like enzymes from a cyanobacterium, a nitrogen-fixing bacterium, a moss, and a primitive plant, horsetail. Results obtained from these studies will lead to a better understanding of the evolution of enzyme family and metabolic pathway in plants and microorganisms. Finally, the moss homologue of anther-specific CHSs may provide insights into the poorly understood process of plant male fertility.