Isonitrile natural products exhibit promising antibacterial activities. However, their mechanism of action (MoA) remains largely unknown. Based on the nanomolar potency of xanthocillin X (Xan) against diverse difficult-to-treat Gram-negative bacteria, including the critical priority pathogen Acinetobacter baumannii, we performed in-depth studies to decipher its MoA. While neither metal binding nor cellular protein targets were detected as relevant for Xan’s antibiotic effects, sequencing of resistant strains revealed a conserved mutation in the heme biosynthesis enzyme porphobilinogen synthase (PbgS). This mutation caused impaired enzymatic efficiency indicative of reduced heme production. This discovery led to the validation of an untapped mechanism, by which direct heme sequestration of Xan prevents its binding into cognate enzyme pockets resulting in uncontrolled cofactor biosynthesis, accumulation of porphyrins, and corresponding stress with deleterious effects for bacterial viability. Thus, Xan represents a promising antibiotic displaying activity even against multidrug resistant strains, while exhibiting low toxicity to human cells.

中文翻译：

---

广谱抗生素黄霉素X有效杀死鲍曼不动杆菌血红素生物合成失调

异腈天然产物表现出有希望的抗菌活性。然而，它们的作用机制 (MoA) 在很大程度上仍然未知。基于黄霉素 X ( Xan ) 对多种难以治疗的革兰氏阴性细菌（包括关键的优先病原体鲍曼不动杆菌）的纳摩尔效力，我们进行了深入研究以破译其 MoA。虽然金属结合和细胞蛋白靶标均未检测到与Xan相关的抗生素效应，耐药菌株的测序揭示了血红素生物合成酶胆色素原合酶 (PbgS) 的保守突变。这种突变导致酶促效率受损，表明血红素产量减少。这一发现验证了一种尚未开发的机制，通过这种机制，Xan 的直接血红素螯合阻止其结合到同源酶袋中，导致不受控制的辅因子生物合成、卟啉的积累和相应的压力，对细菌的生存能力产生有害影响。因此，Xan代表了一种很有前途的抗生素，即使对多药耐药菌株也表现出活性，同时对人体细胞表现出低毒性。