ИСТИНА

The main function of a large family of small heat shock proteins (sHsp or HspB) is binding and preventing aggregation of partially denatured protein substrates. In addition to their chaperone-like activity, sHsp can interact with intact partner proteins and participate in the assembly of supramolecular complexes. It is desirable to separate and separately characterize both these activities. Filamin C (FLNC), a significant component of Z-discs, is a potential protein substrate or protein partner of sHsp. Mechanical stress-induced FLNC denaturation can lead to its aggregation and can result in myo- and/or cardiomyopathies. In addition, the muscle cell requires a specific system which ensures correct packing of FLNC in myofibrillar Z-discs. Human FLNC is a dimer with a monomer molecular weight of about 280 kDa and contains 24 immunoglobulin-like domains (Ig-domains) having a structure similar to the α-crystallin domain (Acd) of sHsp. Therefore, we supposed that FLNC can serve either as a substrate or as a partner protein of sHsp. Our presentation deals with the analysis of the interaction of different sHsp with the C-terminal fragment of FLNC containing 19-24 Ig-domains of FLNC (FLNC19-24). We used recombinant proteins expressed in E.coli and purified by means of ion-exchange and size-exclusion chromatography. Protein-protein interaction was analyzed by means of native electrophoresis, chemical cross-linking, and direct ELISA. Among the four tested sHsp (HspB1, HspB6, HspB7, HspB8) expressed in muscle and cardiac cells, only HspB7 formed stable complexes with FLNC19-24. Isolated AcdB7 also interacted with FLNC19-24 and induced the dissociation of its dimer. Thus, among all the sHsp tested, only HspB7 interacted with FLNC and used this protein as a protein partner. This interaction might be essential for proper packing of FLNC in the Z-disc and its effective functioning. The data from the literature indicate that other sHsp (HspB1, HspB5, and HspB8) can interact with FLNC. However, this might mean that in this case FLNC is used as a protein substrate, but not as a protein partner. The work was supported by Russian Science Foundation (grant 24-74-10008).