Thermodynamic characterization of amyloid polymorphism by Taylor dispersion analysis

Amyloid fibrils of proteins such as α-synuclein are a hallmark of neurodegenerative diseases and much research has focused on their kinetics and mechanisms of formation. The question as to the thermodynamic stability of such structures has received much less attention. Here, we present a novel experimental method to quantify amyloid fibril stability based on chemical depolymerisation and Taylor dispersion analysis. The relative concentrations of fibrils and monomer at equilibrium are determined through an in situ separation of these species through Taylor dispersion in laminar flow inside a microfluidic capillary. This method is highly sample economical, using much less than a microliter of sample per data point and its only requirement is the presence of aromatic residues because of its label-free nature. Using this method, we investigate the differences in thermodynamic stability between different fibril polymorphs of α-synuclein and quantify these differences for the first time. Importantly, we show that fibril formation can be under kinetic or thermodynamic control and that a change in solution conditions can both stabilise and destabilise amyloid fibrils. Taken together, our results establish the thermodynamic stability as a well-defined and key parameter that can contribute towards a better understanding of the physiological roles of amyloid fibril polymorphism.