A Holistic Approach to Understanding Small Heat Shock Protein Mechanism

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ABSTRACT/SUMMARY Cells have numerous strategies to cope with the consequences of stresses that cause protein misfolding and aggregation and lead to formation of plaques, fibrils, and other aggregated species encountered in aging cells, cataract, and neurodegenerative diseases. The protein chaperones known as small heat shock proteins are the cell’s first responders and are therefore key to maintenance of cellular health. Ocular tissues are subjected to stresses such as exposure to UV light, smoking, hypoxia, and ischemia. sHSP function is linked to three of the most prevalent ocular pathologies leading to blindness worldwide: cataract, age-related macular degeneration, and diabetic retinopathy which together account for 65% of world blindness. In lens, sHSPs perform the critical task of maintaining lens transparency and failure to do so is directly linked to cataract. sHSPs are expressed constitutively in retinal cells and are upregulated following injury or stress. Mechanisms used by sHSPs to delay the onset of aggregation of proteins remain enigmatic due to technical challenges posed by sHSPs and the aggregate-prone proteins they protect. Recent developments in the study of disordered proteins and breakthroughs made during the previous period of this long-standing project promise to overcome this critical barrier to mechanistic understanding. Techniques such as NMR, hydrogen-deuterium exchange/mass spectrometry, and covalent cross-linking/mass spectrometry can provide fine-grained information regarding disordered regions of sHSPs that have largely gone uncharacterized but are known to be essential for sHSP activity. The goal of this renewal application is to develop a holistic (“characterized by comprehension of the parts of something as intimately interconnected and explicable only by reference to the whole”) understanding of sHSP structure and function. The effects of stress conditions, modifications, and mutations will be assessed and interpreted in the context of the resultant novel models.