R-type bacteriocins are minimal contractile nanomachines that hold promise as precision antibiotics^1,2,3,4. Each bactericidal complex uses a collar to bridge a hollow tube with a contractile sheath loaded in a metastable state by a baseplate scaffold^1,2. Fine-tuning of such nucleic acid-free protein machines for precision medicine calls for an atomic description of the entire complex and contraction mechanism, which is not available from baseplate structures of the (DNA-containing) T4 bacteriophage⁵. Here we report the atomic model of the complete R2 pyocin in its pre-contraction and post-contraction states, each containing 384 subunits of 11 unique atomic models of 10 gene products. Comparison of these structures suggests the following sequence of events during pyocin contraction: tail fibres trigger lateral dissociation of baseplate triplexes; the dissociation then initiates a cascade of events leading to sheath contraction; and this contraction converts chemical energy into mechanical force to drive the iron-tipped tube across the bacterial cell surface, killing the bacterium.

R 型细菌素是最小的可收缩纳米机器，有望成为精密抗生素^1,2,3,4。^{每个杀菌复合物使用一个项圈来连接一个空心管，该管带有一个由底板支架1,2}以亚稳态加载的收缩护套。对这种用于精准医学的无核酸蛋白质机器进行微调需要对整个复杂和收缩机制进行原子描述，而这在（含 DNA）T4 噬菌体^{5的基板结构中是不可用的}. 在这里，我们报告了完整的 R2 菌素在其收缩前和收缩后状态的原子模型，每个包含 10 种基因产物的 11 个独特原子模型的 384 个亚基。这些结构的比较表明在脓毒蛋白收缩期间发生以下事件序列：尾纤维触发基板三联体的横向解离；然后解离引发一连串导致鞘收缩的事件；这种收缩将化学能转化为机械力，驱动铁尖管穿过细菌细胞表面，杀死细菌。