A Study of Wild Type Alpha Synuclein Binding and Orientation on Gold Nanoparticles.

The disruption of α-synuclein (α-syn) homeostasis in neurons is a potential cause of Parkinson's Disease, which is manifested pathologically by the appearance of α-syn aggregates, or Lewy bodies. Treatments for neurological diseases are extremely limited. In order to study the potential use of gold nanoparticles (Au NPs) to limit α-syn misfolding, the binding and orientation of α-syn on Au NPs was investigated. α-Syn was determined to interact with 20 and 90 nm Au NPs via a multilayered adsorption: a strong electrostatic interaction between α-syn and Au NPs in the hard corona and a weaker non-covalent protein-protein interaction in the soft corona. Spectroscopic and light-scattering titrations led to the determinations of binding constants for the Au NP- α-syn coronas: for the hard corona on 20 nm Au NPs, the equilibrium association constant was 2.9 ± 1.1 x 109 M-1 (for 360 ± 70 α-syn/NP), while on 90 nm Au NP the hard corona association constant was 9.5 ± 0.8 x 1010 M-1 (for 5300 ± 700 α-syn/NP). Binding of the soft corona was thermodynamically unfavorable and kinetically driven, and was in constant exchange with 'free' α-syn in solution. A protease digestion method was used to deduce α-syn orientation and structure on Au NPs, revealing that α-syn absorbs onto negatively charged Au NPs via its N-terminus while apparently retaining its natively unstructured conformation. These results suggest that Au NPs could be used to sequester and regulate α-syn homeostasis.constants for the Au NP- α-syn coronas: for the hard corona on 20 nm Au NPs, the equilibrium association constant was 2.9 ± 1.1 x 109 M-1 (for 360 ± 70 α-syn/NP), while on 90 nm Au NP the hard corona association constant was 9.5 ± 0.8 x 1010 M-1 (for 5300 ± 700 α-syn/NP). Binding of the soft corona was thermodynamically unfavorable and kinetically driven, and was in constant exchange with 'free' α-syn in solution. A protease digestion method was used to deduce α-syn orientation and conformation on Au NPs, revealing that α-syn absorbs onto negatively charged Au NPs via its N-terminus while retaining its natively unstructured conformation. These results suggest that Au NPs could be used to sequester and regulate α-syn homeostasis.