The adhesin FimH is expressed by commensal Escherichia coli and is implicated in urinary tract infections, where it mediates adhesion to mannosylated glycoproteins on urinary and intestinal epithelial cells in the presence of a high-shear fluid environment. The FimH-mannose bond exhibits catch behavior in which bond lifetime increases with force, because tensile force induces a transition in FimH from a compact native to an elongated activated conformation with a higher affinity to mannose. However, the lifetime of the activated state of FimH has not been measured under force. Here we apply multiplexed magnetic tweezers to apply a preload force to activate FimH bonds with yeast mannan, then we measure the lifetime of these activated bonds under a wide range of forces above and below the preload force. A higher fraction of FimH-mannan bonds were activated above than below a critical preload force, confirming the FimH catch bond behavior. Once activated, FimH detached from mannose with multi-state kinetics, suggesting the existence of two bound states with a 20-fold difference in dissociation rates. The average lifetime of activated FimH-mannose bonds was 1000 to 10,000 s at forces of 30–70 pN. Structural explanations of the two bound states and the high force resistance provide insights into structural mechanisms for long-lived, force-resistant biomolecular interactions.

中文翻译：

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FimH-甘露糖非共价键在力下可存活数分钟至数小时


粘附素 FimH 由共生大肠杆菌表达，与尿路感染有关，在高剪切流体环境存在下，它介导与尿液和肠上皮细胞上甘露糖基化糖蛋白的粘附。FimH-甘露糖键表现出捕捉行为，其中键寿命随力增加，因为拉伸力诱导 FimH 从紧凑的天然构象转变为对甘露糖具有更高亲和力的细长活化构象。然而，FimH 的激活状态的寿命尚未在力下测量。在这里，我们应用多路磁镊施加预紧力以激活与酵母甘露聚糖的 FimH 键，然后我们在高于和低于预紧力的广泛力下测量这些激活键的寿命。在临界预紧力之上激活的 FimH-甘露聚糖键的比例高于低于临界预紧力的比率，证实了 FimH 捕获键的行为。一旦被激活，FimH 就以多态动力学从甘露糖上分离出来，表明存在两种结合态，解离速率相差 20 倍。在 30-70 pN 的力下，活化的 FimH-甘露糖键的平均寿命为 1000 至 10,000 秒。对两种结合态和高抗力性的结构解释为长寿命、抗力生物分子相互作用的结构机制提供了见解。