PROS1 and Parkinson disease: Parkinson’s disease (PD) is linked to the aggregation ofthe intrinsically disordered protein α-synuclein (aSyn), butthe precise triggers and mechanisms driving this process remain unclear.Local environmental factors, such as ion concentrations, can influenceaSyn’s conformational ensemble and its tendency to aggregate.In this study, we explore how physiologically relevant ions, mainlyCa2+ and Na+, affect aSyn aggregation, monomerstructural dynamics, and fibril polymorphism.