Chaperone-Like Activity of Human Small Heat Shock Protein-Derived Peptides in Response to Cellular Stress
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Small heat shock proteins (sHsps), a family of molecular chaperones that prevent aggregation of partially unfolded protein substrates, are present in many different organisms across all domains of life. They work to maintain cellular function and survival under stress conditions, such as high temperatures, by binding non-natively folded proteins in an ATP-independent manner. This is followed by either promotion of proper protein folding or facilitation of protein degradation. Malfunction of sHsps in humans has been implicated in the development of several morbidities, particularly in neurological diseases where accumulation of misfolded proteins leads to neurodegeneration. sHsps contain an “alpha-crystallin domain” (ACD) flanked by an N- and C-terminal region (NTR and CTR, respectively) of varying length and sequence. These terminal regions are believed to participate in substrate and quaternary interactions. Their quaternary interactions result in the formation of dynamic oligomers whose physiological relevance and role in chaperone activity has yet to be determined. This work includes two projects, both with aims to identify functional regions of sHsps that contain chaperone activity. In the first, purifying the relatively unstructured N-terminal sequence from human HspB1 and analyzing its interaction with model substrates, we have identified an 88-residue sequence that exhibits chaperone activity in solution. We constructed gold nanoparticles (AuNPs) conjugated to the HspB1 NTR to explore the importance of the oligomeric interactions of the molecular chaperone in binding to its substrate. These sHsp-AuNPs were found to exhibit chaperone activity, with the chaperone capacity varying by substrate and AuNP diameter. Our combined results indicate the particular importance of the NTR in sHsp chaperone activity and demonstrate the therapeutic potential of sHsp-AuNPs. The second project evaluated the chaperone-like activity of mini alpha-Crystallin A (CryAAID1), residues 70-88 of human sHsp alpha-Crystallin A. This peptide was also conjugated to AuNPs and results confirmed CryAAID1 maintained chaperone activity in the absence of other sHsp domains. Substrate specificity AuNP diameter dependence were also demonstrated.