Kong et al. find a touch of romance in the engagement between integrin adhesion receptors and their extracellular matrix ligands. The more life tries to pull them apart, the more they want to stay together.

As a cell crawls along, integrin heterodimers bind extracellular matrix molecules such as fibronectin and help the cell gain traction. You might expect that the harder the integrin–fibronectin bond is pulled, the more likely it is to break. But some types of molecular bond—called catch bonds—actually grow stronger as more force is applied to them.

Researchers have long speculated that integrins might display this unusual behavior, but experiments measuring the forces that disrupt integrin–ligand interactions failed to find any evidence of catch bonds. Kong et al. took a slightly different approach. They used atomic force microscopy to measure how long individual bonds between α5β1 integrin and fibronectin lasted when pulled apart with constant forces. As the pulling force increased, the α5β1–fibronectin association lasted longer, indicating that the molecules do form catch bonds.

The increased force might induce a conformational change in the proteins that locks the bond tighter. Kong et al. provide evidence that this switch occurs in the extracellular head domain of α5β1. Senior author Cheng Zhu, however, speculates that such a conformational change could be propagated across the plasma membrane to the integrin's tail, altering its association with the cytoskeleton and downstream signaling molecules. Force-induced changes in adhesion strength and signaling may help cells migrate and respond to their local environment.

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