Q-DOAS: A Proximity Quenching Assay for Real-Time Detection of Early Protein Aggregation Events

Abstract

Accurate measurement of protein aggregation is essential for studying neurodegenerative diseases. The standard ThT assay reports on amyloid formation but is blind to early oligomers and is prone to interference. We describe Q-DOAS, a plate-reader assay that quantifies protein self-assembly in real time via proximity-quenching of a single, site-specifically conjugated dye (BODIPY-TMR). Using mutant Huntingtin-exon 1 (mHTT-Ex1) and -Synuclein A53T, we show Q-DOAS detects pre-amyloid oligomers, yielding quantitative kinetic data compatible with mechanistic analysis. We demonstrate its utility to dissect mutational effects, screen for protein and small-molecule inhibitors, and quantify amyloid seeding activity in cellular and mouse models of Huntington's disease. Q-DOAS also detects seeds in cerebrospinal fluid from Parkinson's disease patients without amplification. Q-DOAS provides a sensitive, robust, and scalable tool for studying the earliest events in amyloid pathologies and for advancing therapeutic development.