Identification of the Binding Partners for HspB2 and CryAB Reveals Myofibril and Mitochondrial Protein Interactions and Non-Redundant Roles for Small Heat Shock Proteins

• Main Author: Langston, Kelsey Murphey
• Format: Others
• Published: BYU ScholarsArchive 2013
• Subjects: small heat shock proteins (sHSP); HspB2 (MKBP); HspB5 (CryAB); R120G; A177P; molecular chaperones; myocardial maintenance strategies; mitochondria; proteostasis; Microbiology
• Online Access: https://scholarsarchive.byu.edu/etd/3822; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=4821&context=etd

Small Heat Shock Proteins (sHSP) are molecular chaperones that play protective roles in cell survival and have been shown to possess chaperone activity. As such, mutations in this family of proteins result in a wide variety of diseases from cancers to cardiomyopathies. The sHSPs Beta-2 (HspB2) and alpha-beta crystalline (CryAB) are two of the ten human sHSPs and are both expressed in cardiac and skeletal muscle cells. A heart that cannot properly recover or defend against stressors such as extreme heat or cold, oxidative/reductive stress, and heavy metal-induced stress will constantly struggle to maintain efficient function. Accordingly, CryAB is required for myofibril recovery from ischemia/reperfusion (I/R) and HspB2 is required I/R recovery as well as efficient cardiac ATP production. Despite these critical roles, little is known about the molecular function of these chaperones. We have identified over two hundred HspB2-binding partners through both yeast two-hybrid and copurification approaches, including interactions with myofibril and mitochondrial proteins. There is remarkable overlap between the two approaches (80%) suggesting a high confidence level in our findings. The sHSP, CryAB, only binds a subset of the HspB2 interactome, showing that the HspB2 interactome is specific to HspB2 and supporting non-redundant roles for sHSPs. We have confirmed a subset of these binding partners as HspB2 clients via in vitro chaperone activity assays. In addition, comparing the binding patterns and activity of sHSP variants in comparison to wild type can help to elucidate how variants participate in causing disease. Accordingly, we have used Y2H and in vitro chaperone activity assays to compare the disease-associated human variants R120GCryAB and A177PHspB2 to wild type and have identified differences in binding and chaperone function. These results not only provide the first molecular evidence for non-redundancy of the sHSPs, but provides a useful resource for the study of sHSPs in mitochondrial and myofibril function.