HSP27: Mechanisms & Interactions

Hsp27 was initially characterized in response to heat shock as a protein chaperone that facilitates the proper refolding of damaged proteins. The proper chaperoning performance of Hsp27 is achieved by the interaction of Hsp27 with other small Heat shock Proteins but also with several other proteins. Several earlier articles have reported that Hsp27 complexes with HspB5 and HspB6⁷⁰, these complexes detected both in vitro and in vivo can reach a high molecular mass of up to 800 kDa⁷¹. Formation of complexes with HspB6 is temperature dependent and their molecular masses ranges some from 100 to 150 kDa and the others 250 to 300 kDa on equimolar quantities with Hsp27⁷². Hsp27 also interacts with HspB6 and HspB8. Moreover, Hsp27 and its orthologs interact with a number of different model substrate proteins such as citrate synthase, rhodanese, α-glucosidase, insulin, and others forming highly soluble and stable complexes⁷³. Similar highly soluble complexes were described for Hsp27 or its orthologs with many partially denatured enzymes (such as malate dehydrogenase, alcohol dehydrogenase, lactate dehydrogenase, luciferase, and lysozyme) and α-lactalbumin. In addition to these model substrates, Hsp27 interacts with and prevents the aggregation of thermally denatured F-actin and S1 fragment of myosin^74,75. Hsp27 also interacts with intrinsically disordered proteins such as sinuclein and tau proteins, as well as with amyloid peptides, and modulates their irreversible aggregation and development of certain neurodegenerative diseases. All of these data mean that Hsp27 interacts with many different partially denatured or misfolded proteins and prevents their aggregation. This type of interaction might be of great importance in conferring thermo tolerance and resistance to any other types of stress⁷⁶.