On the development of a GroEL based platform for identifying pharmacological chaperones

Abstract

Many protein misfolding diseases are due to changes in protein homeostasis. This might lead to protein misfolding and possibly intra- or extracellular aggregation, causing loss of protein function or gain of toxic function. In several cases, the cellular clearance mechanism is sometimes inhibited and unable to degrade the aggregated forms leading to cell injury and death. This is frequently observed in misfolding diseases like Parkinson's disease, Cystic fibrosis, Alzheimer's, etc. These diseases account for nearly 30-50 % of all known human diseases afflicting millions and have a significant economic impact. However, there are currently few treatments to counteract these diseases. Thus, there is a pressing need to develop strategies to treat these diseases. One strategy is to develop small molecule ligand drugs that prevent the initial protein misfolding reaction. Proteins are somewhat metastable and naturally exist in dynamic equilibria between native fold and an ensemble of partially unfolded forms. This makes the misfolded forms moving targets and thus difficult to stabilize. This difficulty is compounded while developing high throughput assays to screen for stabilizing ligands for these moving protein targets. Consequently, these assays depend on detecting secondary misfolding events such as aggregation or removal of misfolded species, thus increasing the duration of the assays (hours-days). Additionally, in most instances specific cell-based assay systems have to be developed for each misfolding protein. This inhibits the development of broad based assays and complicates rapid screening of the huge compound libraries developed by rational drug design and combinatorial chemistry. In this dissertation, the development of a broad based high throughput assay for identifying novel stabilizers for protein misfolding diseases has been presented. The bacterial chaperonin GroEL binds to proteins that are partially unfolded or exist in a folded to partially folded dynamic equilibrium. Based on this property, the development of a generic broad based assay to probe a multitude of protein substrates based on changes in hydrophobic character was hypothesized and carried out. Using the chaperonin as a detection platform will enable the extension of this detection platform to identify potential stabilizers of the native fold that prevent or inhibit protein misfolding.