Two-piconewton slip bond between fibronectin and the cytoskeleton depends on talin

Mechanical forces on matrix-integrin-cytoskeleton linkages are crucial for cell viability, morphology and organ function(1). The production of force depends on the molecular connections from extracellular-matrix-integrin complexes to the cytoskeleton(2,3). The minimal matrix complex causing integrin-cytoskeleton connections is a trimer of fibronectin's integrin-binding domain FNIII7-10 (ref. 4). Here we report a specific, molecular slip bond that was broken repeatedly by a force of 2 pN at the cellular loading rate of 60 nm s(-1); this occurred with single trimer beads but not with monomer. Talin1, which binds to both integrins and actin filaments in vitro, is required for the 2-pN slip bond and rapid cytoskeleton binding. Further, inhibition of fibronectin binding to alpha(v)beta(3) and deletion of beta(3) markedly decreases the 2-pN force peak. We suggest that talin1 initially forms a molecular slip bond between closely packed fibronectin-integrin complexes and the actin cytoskeleton, which can apply a low level of force to fibronectin until many bonds form or a signal is received to activate a force response.