Identification of Natural Products as Potential Pharmacological Chaperones for Protein Misfolding Diseases.

Defective protein folding and accumulation of misfolded proteins is associated with neurodegenerative, cardiovascular, secretory, and metabolic disorders. Efforts are being made to identify small-molecule modulators or structural-correctors for conformationally destabilized proteins implicated in various protein aggregation diseases. Using a metastable-reporter-based primary screen, we evaluated pharmacological chaperone activity of a diverse class of natural products. We found that a flavonoid glycoside (C-10, chrysoeriol-7-O-ß-D-glucopyranoside) stabilizes metastable proteins, prevents its aggregation, and remodels the oligomers into protease-sensitive species. Data was corroborated with additional secondary screen with disease-specific pathogenic protein. In vitro and cell-based experiments showed that C-10 inhibits α-synuclein aggregation which is implicated in synucleinopathies-related neurodegeneration. C-10 interferes in its structural transition into ß-sheeted fibrils and mitigates α-synuclein aggregation-associated cytotoxic effects. Computational modeling suggests that C-10 binds to unique sites in α-synuclein which may interfere in its aggregation amplification. These findings open an avenue for comprehensive SAR development for flavonoid glycosides as pharmacological chaperones for metastable and aggregation-prone proteins implicated in protein conformational diseases.

Functional competence of a partially engaged GPCR-ß-arrestin complex.

G Protein-coupled receptors (GPCRs) constitute the largest family of cell surface receptors and drug targets. GPCR signalling and desensitization is critically regulated by ß-arrestins (ßarr). GPCR-ßarr interaction is biphasic where the phosphorylated carboxyl terminus of GPCRs docks to the N-domain of ßarr first and then seven transmembrane core of the receptor engages with ßarr. It is currently unknown whether fully engaged GPCR-ßarr complex is essential for functional outcomes or partially engaged complex can also be functionally competent. Here we assemble partially and fully engaged complexes of a chimeric ß2V2R with ßarr1, and discover that the core interaction is dispensable for receptor endocytosis, ERK MAP kinase binding and activation. Furthermore, we observe that carvedilol, a ßarr biased ligand, does not promote detectable engagement between ßarr1 and the receptor core. These findings uncover a previously unknown aspect of GPCR-ßarr interaction and provide novel insights into GPCR signalling and regulatory paradigms.

Emerging Functional Divergence of ß-Arrestin Isoforms in GPCR Function.

G protein-coupled receptors (GPCRs) are tightly regulated by multifunctional protein ß-arrestins. Two isoforms of ß-arrestin sharing more than 70% sequence identity and overall very similar 3D structures, ß-arrestins 1 and 2, were originally expected to be functionally redundant. However, in recent years multiple lines of emerging evidence suggest they have distinct roles in various aspects of GPCR regulation and signaling. We summarize selected examples of GPCRs where ß-arrestin isoforms are discovered to display non-overlapping and sometimes even antagonistic functions. We also discuss potential mechanistic basis for their functional divergence and highlight new frontiers that are likely to form the focal points of research in this area in coming years.