RESUMO
Integrin-mediated adhesion is essential for metazoan life. Integrin binding to ligand requires an activation step prior to binding ligand that depends on direct binding of talin and kindlin to the ß-integrin cytoplasmic tail and the transmission of force from the actomyosin via talin to the integrin-ligand bonds. However, the affinity of talin for integrin tails is low. It is therefore still unclear how such low-affinity bonds are reinforced to transmit forces up to 10 to 40 pN. In this study, we use single-molecule force spectroscopy by optical tweezers to investigate the mechanical stability of the talinâ¢integrin bond in the presence and absence of kindlin. While talin and integrin alone form a weak and highly dynamic slip bond, the addition of kindlin-2 induces a force-independent, ideal talinâ¢integrin bond, which relies on the steric proximity of and the intervening amino acid sequences between the talin- and kindlin-binding sites in the ß-integrin tail. Our findings show how kindlin cooperates with talin to enable transmission of high forces required to stabilize cell adhesion.
Assuntos
Integrinas , Talina , Animais , Talina/metabolismo , Ligantes , Proteínas de Membrana/metabolismo , Adesão CelularRESUMO
Stable anchoring of titin within the muscle Z-disk is essential for preserving muscle integrity during passive stretching. One of the main candidates for anchoring titin in the Z-disk is the actin cross-linker α-actinin. The calmodulin-like domain of α-actinin binds to the Z-repeats of titin. However, the mechanical and kinetic properties of this important interaction are still unknown. Here, we use a dual-beam optical tweezers assay to study the mechanics of this interaction at the single-molecule level. A single interaction of α-actinin and titin turns out to be surprisingly weak if force is applied. Depending on the direction of force application, the unbinding forces can more than triple. Our results suggest a model where multiple α-actinin/Z-repeat interactions cooperate to ensure long-term stable titin anchoring while allowing the individual components to exchange dynamically.