The misfolding of intrinsically disordered proteins (IDPs) such as tau and α-synuclein (αSyn) has been associated with the on-set and progression of Alzheimer’s (AD) and Parkinson’s (PD) diseases. A potential strategy to alleviate the aggregation of IDPs is to maintain / stabilize their native functional state by small molecule binding (pharmacological chaperones). However, the targeting of the native state of IDPs by small molecules has been challenging due to their heterogeneous conformational ensembles.
To tackle this challenge, we initially investigated the structural basis of small molecule drugability of IDPs. Two publicly available monomeric conformational ensembles of Tau were analyzed using in silico structure-based fragment mapping, which identified similar number of hot spots and small molecule binding sites on monomeric Tau ensembles as on tertiary folded proteins of similar size (Kiss et. al. ACS Chem Neurosci., Article, 2018, 9, 12, 2997). Similarly, a structural ensemble of αSyn constructed using experimental NMR data and molecular dynamics simulations was analyzed, which identified diverse set of potential small molecule binding sites, some of which were present at an interface involving relatively long-range tertiary contacts (Toth et. al., Plos One, 2014, 9(2):e87133). Next, we applied two distinct high-throughput chemical microarray surface plasmon resonance imaging screen to detect the binding between small molecules and monomeric full-length Tau (Pickhardt et. al., Current Alzheimer Research, 2015 12, 814) and αSyn (Toth et. al. Scientific Reports, 2019, 18;9(1):16947. The screens identified novel set of drug-like fragment and lead-like compounds that bound to either Tau or α Syn. These results demonstrate that Tau and αSyn are viable receptors of drug-like small molecules.
We verified that selected hit compounds from the screens reduced the aggregation of Tau and α Syn in vitro and in various cell models. Oral administration of selected hit compounds to Drosophila melanogaster, over-expressing full-length wild-type human Tau in their motorneurons, protected them from Tau-induced locomotive impairment by significantly increasing the climbing ability of the flies compared to controls.
Overall, these results support the potential and practical feasibility of the therapeutic strategy to target the monomeric state of IDPs by small molecules to reduce their misfolding and eliminate the formation of potential toxic oligomers. The drug discovery approach presented can be applied to other IDPs linked to other misfolding diseases.
1. Monomeric intrinsically disordered tau and α-synuclein can be viable receptors of drug-like small molecules: structural biology and biophysical perspectives
2. Application of computer-aided structure based and biophysical screening paradigms to identify novel small molecule binders to intrinsically disordered tau and α-synuclein.
3. In vitro and cellular disease models of protein aggregation to characterize the therapeutic effects of discovered novel pharmacological chaperones