Molecular catch bonds are ubiquitous in biology and essential for processes like leucocyte extravasion¹ and cellular mechanosensing². Unlike normal (slip) bonds, catch bonds strengthen under tension. The current paradigm is that this feature provides ‘strength on demand³’, thus enabling cells to increase rigidity under stress^1,4,5,6. However, catch bonds are often weaker than slip bonds because they have cryptic binding sites that are usually buried^7,8. Here we show that catch bonds render reconstituted cytoskeletal actin networks stronger than slip bonds, even though the individual bonds are weaker. Simulations show that slip bonds remain trapped in stress-free areas, whereas weak binding allows catch bonds to mitigate crack initiation by moving to high-tension areas. This ‘dissociation on demand’ explains how cells combine mechanical strength with the adaptability required for shape change, and is relevant to diseases where catch bonding is compromised^7,9, including focal segmental glomerulosclerosis¹⁰ caused by the α-actinin-4 mutant studied here. We surmise that catch bonds are the key to create life-like materials.

分子捕捉键在生物学中无处不在，对于白细胞外渗¹和细胞机械传感²等过程至关重要。与普通（滑动）键不同，捕捉键在张力下会加强。当前的范例是，此功能提供“按需强度³ ”，从而使细胞能够在压力^{1、4、5、6}下增加刚性。然而，捕获键通常比滑动键弱，因为它们具有通常被掩埋的神秘结合位点^7,8. 在这里，我们表明捕获键使重组的细胞骨架肌动蛋白网络比滑动键更强，即使单个键较弱。模拟表明，滑动键仍然被困在无应力区域，而弱结合允许捕捉键通过移动到高张力区域来减轻裂纹萌生。这种“按需解离”解释了细胞如何将机械强度与形状变化所需的适应性结合起来，并且与捕捉结合受损的疾病相关^7,9 ，包括此处研究的 α-actinin-4 突变体引起的局灶节段性肾小球硬化¹⁰ . 我们推测捕捉键是创造栩栩如生的材料的关键。