Characterization of binary and ternary complexes of filamin A domain FLNa-Ig21 with cytosolic tails of αMβ2 integrin

Abstract

Integrins are a/B heterodimeric transmembrane receptors important for cell adhesion and migration. The cytosolic tails of integrin are essential for signalling and maintenance of its resting state. Integrin binding partners interact with the tails to control integrin activation, particularly the B tail. Filamin A is known to negatively regulate B2 integrins via its 21st domain (FLNa-Ig21). B2 integrins are important in leukocytes. Amongst the B2 integrins, aMB2 is a promiscuous receptor known to have multiple roles in immune response. While much is known about the interaction between the B2 cytosolic tail and FLNa-Ig21, its counterpart has yet to be characterized. Recent studies reported a novel interaction between aM cytosolic tail and FLNa-Ig21, and also a possible ternary complex involving both tails. However, atomic-resolution structure study was unsuccessful due to low-affinity interaction. We achieved stable binary complexes of FLNa-Ig21 with aM and b2 cytosolic tails which was amenable for structural analyses by NMR. Target proteins were recombinantly expressed, purified, and extensively characterized. We report that aM tail can interact with FLNa-Ig21, and a ternary complex of FLNa-Ig21 with both aM and B2 cytosolic tails was detected. Our study offers insights to structural properties of aM cytosolic tail when bound to FLNa-Ig21.