Structure of three tandem filamin domains reveals auto-inhibition of ligand binding

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Abstract
Human filamins are large actin‐crosslinking proteins composed of an N‐terminal actin‐binding domain followed by 24 Ig‐like domains (IgFLNs), which interact with numerous transmembrane receptors and cytosolic signaling proteins. Here we report the 2.5 Å resolution structure of a three‐domain fragment of human filamin A (IgFLNa19–21). The structure reveals an unexpected domain arrangement, with IgFLNa20 partially unfolded bringing IgFLNa21 into close proximity to IgFLNa19. Notably the N‐terminus of IgFLNa20 forms a β‐strand that associates with the CD face of IgFLNa21 and occupies the binding site for integrin adhesion receptors. Disruption of this IgFLNa20–IgFLNa21 interaction enhances filamin binding to integrin β‐tails. Structural and functional analysis of other IgFLN domains suggests that auto‐inhibition by adjacent IgFLN domains may be a general mechanism controlling filamin–ligand interactions. This can explain the increased integrin binding of filamin splice variants and provides a mechanism by which ligand binding might impact filamin structure.

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