Using a technique they invented called molecular-tension-based fluorescence microscopy, researchers at Emory University have observed that a cell receptor called integrin forms a surprisingly strong attachment to one of its usual peptide binding partners (Biophys. J. 2014, DOI: 10.1016/j.bpj.2014.01.049). How cells respond to external forces and chemical cues is something researchers—particularly those designing drugs targeted at tumor cells—have long been trying to understand and control. Integrin has been of special interest because it resides in cell membranes and plays a crucial role in attaching cells to their surroundings. Emory’s Khalid S. Salaita and coworkers were recently attempting to measure the force integrin exerts on an RGD peptide when they made their discovery. Integrins studding the outside of breast cancer cells pulled so hard on peptides tethered to a surface that the receptors ripped the peptides—tether and all—off the substrate. Salaita says this result is unexpected because he and his team anchored the peptides to the surface via a biotin-streptavidin linkage, the strongest noncovalent interaction known in nature. Biotin is a vitamin important to cell growth, and streptavidin is a protein. One explanation for the result, Salaita says, might be that multiple integrins cluster together where the cells adhere to the surface and cooperate to generate an extreme force.