Akey David L, Kittendorf Jeffrey D, Giraldes John W, Fecik Robert A, Sherman David H, Smith Janet L
Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, Michigan 48109-2216, USA.
Nat Chem Biol. 2006 Oct;2(10):537-42. doi: 10.1038/nchembio824. Epub 2006 Sep 10.
Polyketides are a class of biologically active microbial and plant-derived metabolites that possess a high degree of structural and functional diversity and include many human therapeutics, among them anti-infective and anti-cancer drugs, growth promoters and anti-parasitic agents. The macrolide antibiotics, characterized by a glycoside-linked macrolactone, constitute an important class of polyketides, including erythromycin and the natural ketolide anti-infective agent pikromycin. Here we describe new mechanistic details of macrolactone ring formation catalyzed by the pikromycin polyketide synthase thioesterase domain from Streptomyces venezuelae. A pentaketide phosphonate mimic of the final pikromycin linear chain-elongation intermediate was synthesized and shown to be an active site affinity label. The crystal structures of the affinity-labeled enzyme and of a 12-membered-ring macrolactone product complex suggest a mechanism for cyclization in which a hydrophilic barrier in the enzyme and structural restraints of the substrate induce a curled conformation to direct macrolactone ring formation.
聚酮化合物是一类具有生物活性的微生物和植物源代谢产物，具有高度的结构和功能多样性，包括许多用于人类治疗的药物，其中有抗感染药、抗癌药、生长促进剂和抗寄生虫剂。以糖苷连接的大环内酯为特征的大环内酯类抗生素是聚酮化合物的一个重要类别，包括红霉素和天然酮内酯抗感染药匹克霉素。在此，我们描述了委内瑞拉链霉菌产生的匹克霉素聚酮合酶硫酯酶结构域催化大环内酯环形成的新机制细节。合成了匹克霉素最终线性链延伸中间体的五酮膦酸酯模拟物，并证明其为活性位点亲和标记物。亲和标记酶和12元环大环内酯产物复合物的晶体结构表明了一种环化机制，即酶中的亲水屏障和底物的结构限制诱导卷曲构象以指导大环内酯环的形成。
