C-Terminal Fragment of Filamin C Containing Immunoglobulin-Like Domains 19-24 Selectively Interacts with the Small Heat Shock Protein HspB7.

Filamin C is an adapter protein involved in the regulation of cytoskeleton; it interacts with more than 90 protein partners, including small heat shock proteins (sHsps). However, the details of filamin C interaction with sHsps remain poorly characterized. Here, we used immunochemistry methods, size-exclusion chromatography, native gel electrophoresis, and chemical crosslinking to investigate the interactions of a long C-terminal fragment of filamin C containing immunoglobulin (Ig)-like domains 19-24 (FLNC19-24) with sHsps. Out of five analyzed sHsps (HspB1, phosphorylation-mimicking 3D mutant of HspB1, HspB5, HspB6, HspB7, and HspB8), only HspB7 formed complexes with FLNC19-24. Taking into account that HspB7 interacted with the isolated Ig-like domain 24 and filamin fragments containing Ig-like domains 22-24 and 19-24, we concluded that HspB7 is a bona fide partner of filamin C. Selective binding of the α-crystallin domain of HspB7 with the Ig-like domain 24 induced dissociation of filamin dimers, which might promote filamin C translocation in the cell and facilitate the repairs of damaged contractile apparatus.