Fig. 7: Both talin dimerization and talin–paxillin–kindlin pathway contribute to integrin activation.

a PAC-1-binding assay showing that integrin activation by full-length active talin (tlnM3) was reduced by deletion of talin-dimerization domain (tlnM3 DDdel), and addition of paxillin-binding mutations (tlnM3 R2R8R11mut) further reduced PAC-1 binding to almost the level caused by talin head (tlnH) only. *p = 0.0416 with 95% confidence interval −4.267 to −0.0963 (t-test); ***p = 0.0003 with 95% confidence interval −6.453 to −2.529; N = 6 biologically independent samples. Values are shown as mean ± S.E.M. b Synergy between intact kindlin-2 and intact active talin (tlnM3 + K2FL) was significantly impaired by DDdel as shown by reduced PAC-1 binding. Combination of paxillin-binding deficient mutations and DDdel mutation further substantially reduced PAC-1 binding. *p = 0.0286 with 95% confidence interval −6.485 to −0.4448 (t-test), N = 3 biologically independent samples; ****p < 0.0001 with 95% confidence interval −13.40 to −7.084 (t-test), N = 6 biologically independent samples. Values are given as mean ± S.E.M. c A model for dynamic integrin-activation process where inactive talin first engages with PIP2 to initiate, via talin-H, the conformational opening of talin, which initiates the recruitment of paxillin (Step 1). At Step 2, activated talin dimer, while anchored to PIP2 membrane, clusters two conformationally open integrins (i1 and i2) via each talin monomer subunit. Meanwhile, talin, which is bound to integrin i1, links, via paxillin, to kindlin that is bound to another integrin i2. Such talin–paxillin–kindlin linkage (primarily driven by talin-R as shown in the text) strengthens the talin-dimer-induced microclustering of integrins, leading to their potent multivalent binding and efficient FA assembly for cell adhesion. a, b Raw data are provided in Source Data file.