Calpain Cleavage Promotes Talin Binding to the β3 Integrin Cytoplasmic Domain

Abstract

Talin links integrin β cytoplasmic domains to the actin cytoskeleton and is involved in the clustering and activation of these receptors. To understand how talin recognizes integrin β cytoplasmic domains, we configured surface plasmon resonance methodology to measure the interaction of talin with the β3 integrin cytoplasmic domain. Here we report that the N-terminal ∼47-kDa talin head domain (talin-H) has a 6-fold higher binding affinity than intact talin for the β3 tail. The affinity difference is mainly due to a difference in kon. Calpain cleavage of intact talin released talin-H and resulted in a 16-fold increase in apparent Ka and a 100-fold increase in apparent kon. The increase in talin binding after cleavage was greater than predicted for stoichiometric liberation of free talin-H. This additional increase in binding was due to cooperative binding of talin-H and talin rod domain to the β3 tail. Talin resembles ERM (ezrin, radixin, moesin) proteins in possessing an N-terminal FERM (band four-point-one, ezrin, radixin, moesin) domain. These data show that the talin FERM domain, like that in the ERM proteins, is masked in the intact molecule. Furthermore, they suggest that talin cleavage by calpain may contribute to the effects of the protease on the clustering and activation of integrins.