The structural basis of the Talin-KANK1 interaction that coordinates the actin and microtubule cytoskeletons at focal adhesions.

Abstract

Adhesion between cells and the extracellular matrix (ECM) is mediated by heterodimeric ({beta}) integrin receptors that are intracellularly linked to the contractile actomyosin machinery. One of the proteins that control this link is talin, which organises cytosolic signalling proteins into discrete complexes on {beta}-integrin tails referred to as focal adhesions (FAs). The adapter protein KANK1 binds to talin in the region of FAs known as the adhesion belt. Here, we developed a novel crystallographic method to resolve the talin-KANK1 complex. This structure revealed that the talin binding KN motif of KANK1 has a novel fold, where a {beta}-turn stabilises the -helical region, explaining its specific interaction with talin R7 and high affinity. Single point mutants in KANK1 identified from the structure abolished the interaction and enabled us to examine KANK1 enrichment in the adhesion belt. Strikingly, in cells expressing a constitutively active form of vinculin that keeps the FA structure intact even in the presence of myosin inhibitors, KANK1 localises throughout the entire FA structure even when actomyosin tension is released. We propose a model whereby actomyosin forces on talin eliminate KANK1 from talin binding in the centre of FAs while retaining it at the adhesion periphery.