Keith Ballard



Small heat shock proteins (sHSPs) and related vertebrate α-crystallins are a ubiquitous class of ATP-independent molecular chaperones with a monomeric molecular mass of 12-42 kDa. These protiens exhibit increased expression during high temperature stress, but are also induced in response to ischemic injury, oxidative stress, exposure to heavy metals and a variety of other stresses that cause protein denaturation and aggregation in a living cell. Most sHSPs have a native oligomeric form of 12 to >32 monomeric subunits. In our current model, heat stress facilitates the dissociation of sHSP oligomers into an active species with a hydrophobic surface capable of binding exposed hydrophobic patches on denaturing client proteins, preventing their irreversible aggregation. Other ATP-dependent chaperones are believed to interact with sHSP-substrate complexes to initiate the refolding of non-native sHSP-stabilized substrate. Mutations and/or expression defects in sHSPs have been linked to a variety of diseases such as, cataract, cardiac and skeletal myopathies, and neurodegenerative disorders. Despite extensive data resulting from structural and biochemical analysis of sHSPs, a model that identifies and fully elucidates sHSP-substrate interactions, in addition to possible interactions with other chaperones of the protein quality control network has yet to be constructed. We propose using p-benzoyl-phenylalanine (p-Bpa), a UV-inducible cross-linker, coupled with MS/MS analysis to identify potential substrate binding sites in all domains of the wheat TaHSP16.9 dodecamer and to determine how DnaK binds sHSP-captured substrates. These data will be used to compare similar studies performed with pea PsHSP18.1 in order to develop a comprehensive model capable of characterizing how sHSPs recognize and bind substrate, in addition to interactions involving sHSPs and other components of the protein quality control network, which are important for controlling cellular damage inflicted by stress and disease.