Division of Medicinal Chemistry, College of Pharmacy, and Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
J Am Chem Soc. 2009 Dec 23;131(50):18066-8. doi: 10.1021/ja907307h.
The azicemicins, which are angucycline-type antibiotics produced by the actinomycete, Kibdelosporangium sp. MJ126-NF4, contain an aziridine ring attached to the polyketide core. Feeding experiments using [1-(13)C]acetate or [1,2-(13)C(2)]acetate indicated that the angucycline skeleton is biosynthesized by a type II polyketide synthase. Isotope-tracer experiments using deuterium-labeled amino acids revealed that aspartic acid is the precursor of the aziridine moiety. Subsequent cloning and sequencing efforts led to the identification of the azicemicin (azic) gene cluster spanning approximately 50 kbp. The cluster harbors genes typical for type II polyketide synthesis. Also contained in the cluster are genes for two adenylyl transferases, a decarboxylase, an additional acyl carrier protein (ACP), and several oxygenases. On the basis of the assigned functions of these genes, a possible pathway for aziridine ring formation in the azecimicins can now be proposed. To obtain support for the proposed biosynthetic pathway, two genes encoding adenylyltransferases were overexpressed and the resulting proteins were purified. Enzyme assays showed that one of the adenylyltransferases specifically recognizes aspartic acid, providing strong evidence, in addition to the feeding experiments, that aspartate is the precursor of the aziridine moiety. The results reported herein set the stage for future biochemical studies of aziridine biosynthesis and assembly.
氮杂霉素是由放线菌 Kibdelosporangium sp. MJ126-NF4 产生的安格环型抗生素，其中含有一个连接在聚酮核心上的氮杂环丙烷环。使用 [1-(13)C]乙酸或 [1,2-(13)C(2)]乙酸进行的喂养实验表明，安格环骨架是由 II 型聚酮合酶生物合成的。使用氘标记的氨基酸进行的同位素示踪实验表明，天冬氨酸是氮杂环丙烷部分的前体。随后的克隆和测序工作导致鉴定了大约 50 kbp 的氮杂霉素 (azic) 基因簇。该簇包含 II 型聚酮合成的典型基因。该簇还包含两个腺苷酰转移酶、一个脱羧酶、一个额外的酰基载体蛋白 (ACP) 和几个加氧酶的基因。根据这些基因的功能，现在可以提出氮杂霉素中环氮形成的可能途径。为了获得对提议的生物合成途径的支持，我们过表达了两个编码腺苷酰转移酶的基因，并对得到的蛋白质进行了纯化。酶促实验表明，其中一个腺苷酰转移酶特异性识别天冬氨酸，除了喂养实验外，这为天冬氨酸是氮杂环丙烷部分的前体提供了强有力的证据。本文的结果为未来的氮杂环生物合成和组装的生化研究奠定了基础。
