Speaker
Description
Fibrillar aggregates of disordered proteins are a key feature of many diseases and also play diverse functional roles. The current state of the art for deducing protein aggregation mechanisms involves globally fitting concentration-dependent fibril growth kinetics to analytical models to infer the most plausible mechanism. Such analyses applied to many different proteins find that secondary processes (such as nucleation induced by large aggregates, or fragmentation of large aggregates into smaller pieces) most often dominate the kinetics, especially when there is a significant lag phase followed by rapid growth. By using the new method of mass photometry--based on interferometric light scattering measurements from single molecules in solution--to directly monitor the real-time evolution of oligomer populations during the aggregation cascade, we show that the standard analysis approach does not properly capture the aggregation mechanism. Studying tau protein, we globally fit not only the growth/decay kinetics for every oligomer population observed by mass photometry, but also the fibril kinetics monitored by ThT fluorescence, providing the first quantitative model of aggregation kinetics across all stages of the cascade based on direct observation.