Keratinicyclins and keratinimicins are recently discovered glycopeptide antibiotics. Keratinimicins show broad-spectrum activity against Gram-positive bacteria, while keratinicyclins form a new chemotype by virtue of an unusual oxazolidinone moiety and exhibit specific antibiosis against Clostridioides difficile. Here we report the mechanism of action of keratinicyclin B (KCB). We find that steric constraints preclude KCB from binding peptidoglycan termini. Instead, KCB inhibits C. difficile growth by binding wall teichoic acids (WTAs) and interfering with cell wall remodeling. A computational model, guided by biochemical studies, provides an image of the interaction of KCB with C. difficile WTAs and shows that the same H-bonding framework used by glycopeptide antibiotics to bind peptidoglycan termini is used by KCB for interacting with WTAs. Analysis of KCB in combination with vancomycin (VAN) shows highly synergistic and specific antimicrobial activity, and that nanomolar combinations of the two drugs are sufficient for complete growth inhibition of C. difficile, while leaving common commensal strains unaffected.

角蛋白环素和角蛋白霉素是最近发现的糖肽抗生素。角蛋白霉素对革兰氏阳性菌表现出广谱活性，而角蛋白环素则凭借不寻常的恶唑烷酮部分形成新的化学型，并对艰难梭菌表现出特异性抗菌作用。在这里，我们报告了角蛋白环素 B (KCB) 的作用机制。我们发现空间限制阻止 KCB 结合肽聚糖末端。相反，KCB 通过结合壁磷壁酸 (WTA) 并干扰细胞壁重塑来抑制艰难梭菌生长。以生化研究为指导的计算模型提供了 KCB 与艰难梭菌 WTA 相互作用的图像，并表明 KCB 使用与糖肽抗生素结合肽聚糖末端相同的氢键框架来与 WTA 相互作用。 KCB 与万古霉素 (VAN) 组合的分析显示出高度协同和特异性的抗菌活性，并且两种药物的纳摩尔组合足以完全抑制艰难梭菌的生长，同时使常见的共生菌株不受影响。