Life Sciences Institute, University of Michigan , 210 Washtenaw Avenue, Ann Arbor, Michigan 48109, United States.
J Am Chem Soc. 2014 Jan 29;136(4):1579-86. doi: 10.1021/ja4115924. Epub 2014 Jan 17.
Siderophores are high-affinity iron chelators produced by microorganisms and frequently contribute to the virulence of human pathogens. Targeted inhibition of the biosynthesis of siderophores staphyloferrin B of Staphylococcus aureus and petrobactin of Bacillus anthracis hold considerable potential as a single or combined treatment for methicillin-resistant S. aureus (MRSA) and anthrax infection, respectively. The biosynthetic pathways for both siderophores involve a nonribosomal peptide synthetase independent siderophore (NIS) synthetase, including SbnE in staphyloferrin B and AsbA in petrobactin. In this study, we developed a biochemical assay specific for NIS synthetases to screen for inhibitors of SbnE and AsbA against a library of marine microbial-derived natural product extracts (NPEs). Analysis of the NPE derived from Streptomyces tempisquensis led to the isolation of the novel antibiotics baulamycins A (BmcA, 6) and B (BmcB, 7). BmcA and BmcB displayed in vitro activity with IC50 values of 4.8 μM and 19 μM against SbnE and 180 μM and 200 μM against AsbA, respectively. Kinetic analysis showed that the compounds function as reversible competitive enzyme inhibitors. Liquid culture studies with S. aureus , B. anthracis , E. coli , and several other bacterial pathogens demonstrated the capacity of these natural products to penetrate bacterial barriers and inhibit growth of both Gram-positive and Gram-negative species. These studies provide proof-of-concept that natural product inhibitors targeting siderophore virulence factors can provide access to novel broad-spectrum antibiotics, which may serve as important leads for the development of potent anti-infective agents.
铁载体是微生物产生的高亲和力铁螯合剂，通常有助于人类病原体的毒力。靶向抑制金黄色葡萄球菌 staphyloferrin B 和炭疽芽孢杆菌 petrobactin 的生物合成，分别作为耐甲氧西林金黄色葡萄球菌 (MRSA) 和炭疽感染的单一或联合治疗方法具有相当大的潜力。这两种铁载体的生物合成途径都涉及非核糖体肽合成酶独立铁载体 (NIS) 合成酶，包括 staphyloferrin B 中的 SbnE 和 petrobactin 中的 AsbA。在这项研究中，我们开发了一种针对 NIS 合成酶的生化测定法，以筛选针对 SbnE 和 AsbA 的抑制剂，该抑制剂针对海洋微生物衍生天然产物提取物 (NPE) 文库。对来自链霉菌 tempisquensis 的 NPE 的分析导致了新型抗生素 baulamycins A (BmcA, 6) 和 B (BmcB, 7) 的分离。BmcA 和 BmcB 在体外对 SbnE 的活性具有 IC50 值分别为 4.8 μM 和 19 μM，对 AsbA 的活性分别为 180 μM 和 200 μM。动力学分析表明，这些化合物作为可逆竞争性酶抑制剂发挥作用。金黄色葡萄球菌、炭疽芽孢杆菌、大肠杆菌和其他几种细菌病原体的液体培养研究表明，这些天然产物能够穿透细菌屏障并抑制革兰氏阳性和革兰氏阴性物种的生长。这些研究提供了概念验证，即针对铁载体毒力因子的天然产物抑制剂可以提供新型广谱抗生素的途径，这些抗生素可能成为开发有效抗感染药物的重要先导化合物。
