Many diverse diseases, including cataract, some types of glaucoma, Alzheimer disease, diabetes and cancer to name only a few, are now known to share the common feature of aggregated, misfolded or modified protein deposits. The pathological hallmark in this group of diseases is protein aggregation and deposition in specific cells, tissues or organs. The pathological similarities indicate that common principles that govern protein interactions underlie protein misfolding degenerative diseases. Cataract is a classic example of a protein misfolding and aggregation disease. Cataract, a major cause of blindness in the world, develops as a result of age-related modifications and aggregation of the lens proteins. ?-crystallin accounts for nearly 40% of the adult lens proteins but its structure-function is yet to be fully understood. The chaperone-like activity of ?-crystallin is believed to play a central role in maintaining lens transparency. During aging, lens crystallins undergo truncation and these modifications correlate with lens crystallin aggregations responsible for light scattering. It is well established that the addition of ?-crystallin to aggregating proteins stops a further increase in aggregation and light scattering. We have demonstrated that specific sequences in ?-crystallin subunits suppress aggregation of denaturing proteins. However, the full potential of ?-crystallin-derived peptides (mini-chaperones) is yet to be realized. To enhance our understanding of the role of non-native interactions in cataract formation, we propose the following specific aims:
Aim 1. Identify the sequences involved in abnormal interactions of ?A-crystallin subunits that lead to protein aggregation in human cataract-causing ?A-crystallin mutants (?AR49C, ?AF71V, ?AG98R and ?AR116H) using novel deuterated cross linkers, biotynylated reagents and peptide arrays.
Aim 2. Determine the mechanism and efficacy of ?A-crystallin-derived mini-chaperone in preventing the aggregation of metastable ?A- crystallins (mutants and truncated crystallins) and restoring chaperone activity.
The specific aims will be accomplished using novel cross-linkers and mass spectrometric methods. We will also use site-directed mutagenesis and cell culture expression and analysis systems to confirm the cross linking data. These innovative studies will give us new insights into potential interventions for protein misfolding diseases, not only of the eye but also of other parts of the body.
Cataract and a host of other diseases result from abnormal interaction of proteins in the cells. The goals of this research are to understand lens protein aggregation in cataract formation and to develop and test lens protein ?-crystallin-derived peptide as active mini-chaperones capable of suppressing protein aggregation. Understanding the structural changes in mutant proteins associated with cataract can help us learn why certain mutations in lens crystallins lead to cataract. Restoring the lost function in mutant crystallins may control the lens protein aggregation that characterizes cataract formation. Previous studies have shown that peptide chaperones stabilize unfolded proteins. This project will test the ability of peptide chaperones to stabilize and restore activity in mutant and modified lens crystallins.
|Santhoshkumar, Puttur; Karmakar, Srabani; Sharma, Krishna K (2016) Structural and functional consequences of chaperone site deletion in ?A-crystallin. Biochim Biophys Acta 1864:1529-38|
|Raju, Murugesan; Santhoshkumar, Puttur; Krishna Sharma, K (2016) Alpha-crystallin-derived peptides as therapeutic chaperones. Biochim Biophys Acta 1860:246-51|
|Raju, Murugesan; Santhoshkumar, Puttur; Xie, Leike et al. (2014) Addition of ?A-crystallin sequence 164-173 to a mini-chaperone DFVIFLDVKHFSPEDLT alters the conformation but not the chaperone-like activity. Biochemistry 53:2615-23|