Significance: Kindlin proteins play crucial roles in the integrin-signaling pathway by directly interacting with and activating integrins, which mediate the cell–extracellular matrix adhesion and signaling. Mutations of kindlins lead to diseases, such as Kindler syndrome, associated with skin blistering and atrophy; leukocyte adhesion deficiency; and cancers. However, the molecular basis underlying kindlin-mediated integrin activation remains to be determined. Here, we report the structural basis of the specific interaction between kindlins and integrins. Furthermore, we demonstrate that kindlins synergize integrin activation by forming a dimer, providing a model for understanding integrin signaling. Finally, we interpret disease-causing mutations found in kindlins at the atomic level, which can be useful for understanding and treating these diseases.

Ankyrin adaptors together with their spectrin partners coordinate diverse ion channels and cell adhesion molecules within plasma membrane domains and thereby promote physiological activities including fast signaling in the heart and nervous system. Ankyrins specifically bind to numerous membrane targets through their 24 ankyrin repeats (ANK repeats), although the mechanism for the facile and independent evolution of these interactions has not been resolved. Here we report the structures of ANK repeats in complex with an inhibitory segment from the C-terminal regulatory domain and with a sodium channel Nav1.2 peptide, respectively, showing that the extended, extremely conserved inner groove spanning the entire ANK repeat solenoid contains multiple target binding sites capable of accommodating target proteins with very diverse sequences via combinatorial usage of these sites. These structures establish a framework for understanding the evolution of ankyrins' membrane targets, with implications for other proteins containing extended ANK repeat domains.