α-Synuclein's adsorption, conformation, and orientation on cationic gold nanoparticle surfaces seeds global conformation change

α-Synuclein (α-syn), an aggregation-prone amyloid protein, has been suggested as a potential cause of Parkinson's disease. When misfolded, α-syn aggregates as Lewy bodies in the brain, the loss of which can disrupt protein homeostasis. To investigate the potential of nanoparticle-mediated therapy for amyloid diseases, α-syn adsorption onto positively charged poly(allylamine hydrochloride) coated gold nanoparticles (PAH Au NPs) was studied. α-Syn adsorbs in multilayers onto PAH Au NPs, which with increasing α-syn/PAH Au NP ratios (>2000 α-syn/PAH Au NP) results in the flocculation and sedimentation of α-syn coated PAH Au NPs. The orientation and conformation of α-syn on PAH Au NPs were studied using trypsin digestion and circular dichroism, which showed that α-syn adopts a random orientation on PAH Au NPs, with an increase in β-sheet and a decrease in α-helix structures. A consistent global change in α-syn's conformation was also observed regardless of PAH Au NP concentration, suggesting bound α-syn initiates conformational changes to free α-syn.