Protein-protein interactions of Hsp27

Author(s): Freilich, Rebecca | Advisor(s): Gestwicki, Jason E | Abstract: Small Heat Shock Proteins (sHSPs), including Hsp27, are a non-enzymaticclass of molecular chaperones that bind improperly folded proteins and maintain theirsolubility, acting as a first line of defense against cellular stress. Through their ‘holdase’function, the sHSPs are implicated in a variety of diseases that involve imbalances inprotein homeostasis, such as cancer and neurodegeneration. However, because theyform highly dynamic, polydisperse oligomers, it has been difficult to study how they workand even what they interact with. This thesis explores the various protein-proteininteractions (PPIs) that involve the sHSPs (particularly Hsp27) as a way to clarify sHSPfunction and guide future small-molecule development. Chapter one consists of areview of the various PPIs within the chaperone network and highlights the critical roleof PPIs in facilitating cooperation between chaperone families, and how these individualPPIs represent important targets for small-molecule discovery. Chapter two describes acollaborative effort to characterize how point mutations within the Hsp70-sHSP adaptorprotein BAG3 can upend the function of the entire network and lead to disease.Chapter three describes the characterization of Hsp27’s interaction with client proteinTau and the important finding that client-binding sites are competitive with oligomericPPIs. Taken together, this work emphasizes the importance of individual interactioninterfaces in dictating function of a chaperone itself and in the context of the greaternetwork.