The FERM domain of kindlin-3 exhibits a monomeric and cloverleaf-like structure. (A) The organization of kindlin-3’s subdomains. The truncated regions in kindlin-3Δ and kindlin-3Δ’ were indicated. Ribbon representations of kindlin-3Δ (B) and kindlin-3Δ’ (C), in which the subdomains are labeled and colored using the similar or same color pattern as shown in panel A. (D) Superimposition of the structures of kindlin-3Δ and kindlin-3Δ’. (E) Structural comparison of kindlin-3Δ’ (color coded) and kindlin-2Δ’ (gray). The missing loop region in the F2 of kindlin-3Δ’ is indicated by hypothetical dotted line while the visible and fixed loop of the same region in kindlin-2Δ’ is highlighted in red. (F) Structural comparison of kindlin-3Δ (color coded) and the kindlin-2Δ dimer (gray and pink). The F2 subdomain-swapped dimer formed in kindlin-2Δ is not observed in kindlin-3Δ. (G) Analytic gel filtration analysis to show the monomeric property of kindlin-3Δ protein in solution at different storage time, either freshly purified protein (0 day) or the same batch of protein placed at 4°C for 3 or 10 days. (H) Integrin αIIbβ3 activation induced by coexpression of DsRed-fused talin head (TH) with EGFP-kindlins (K1, K2, and K3) was evaluated by using the PAC-1 binding assay in transfected CHO-αIIbβ3 cells. (I) The effect of GST-fused EGFP–kindlin-3 (GST-K3) on integrin αIIbβ3 activation was evaluated using the PAC-1 binding assay. (J) Dimerization of GST-fused EGFP–kindlin-3 (GST-K3) was confirmed by the DSS crosslinking assay and western blotting. EGFP–kindlin-3 (K3) was used as a control. Results present the mean ± standard deviation of 3 experiments. **P < .01. ns, nonsignificant.