Broad Spectrum Antibiotic Xanthocillin X Effectively Kills Acinetobacter baumannii via Dysregulation of Heme Biosynthesis

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.

异腈类天然产物展现出潜在的抗菌活性。然而，其作用机制（MoA）尚不明确。基于黄连素X（Xan）对多种难以治疗的革兰氏阴性菌，包括关键优先病原体鲍曼不动杆菌，具有纳米摩尔有效浓度的特性，我们对Xan的作用机制进行了深入研究。尽管未检测到金属结合或细胞蛋白靶点与Xan的抗菌作用相关，但对耐药菌株的测序揭示了血红素生物合成酶前卟啉原合酶（PbgS）中存在一个保守突变。这一突变导致酶的催化效率下降，表明血红素产量减少。这一发现引导我们验证了一种未被开发的机制，即Xan通过直接夺取血红素，防止其与同源酶活性位点结合，从而阻止辅因子的无序生物合成，导致卟啉积累以及相应的应激反应，对细菌的存活产生有害影响。因此，Xan是一种具有潜力的抗生素，即使对多重耐药菌株也显示出活性，同时对人类细胞毒性较低。