Transient Protein-Protein Interactions in the IDP Alpha-Synuclein Detected by NMR: Implications for Protein Aggregation

Abstract

BioMaPS Institute for Quantitative Biology and Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ, 08854. NMR paramagnetic relaxation enhancement experiments (PREs) have been applied to the intrinsically disordered protein alpha-synuclein, the primary protein in Parkinson's disease, to directly characterize transient intermolecular complexes at neutral and low pH as well as ionic strength-dependent solutions at pH 6.0. At neutral pH, we observed weak N- to C-terminal inter-chain contacts that are driven by electrostatic interactions while at low pH, C- to C-terminal inter-chain interactions are significantly stronger and driven by hydrophobic contacts. In addition to the pH-dependent transient self-associated alpha-synuclein complex, we also detected the changes of transient protein-protein interactions of alpha-synyclein in solution at varied [NaCl] (0-500 mM). By using titration-based PRE experiments, we have calculated approximate 6% and 2% transient head-to-tail complexes of alpha-synuclein in solution without and with the addition of 100 mM NaCl, respectively. The results presented here show that 1H NMR paramagnetic relaxation experiments are a powerful tool for visualizing transient low-populated initial encounter complexes in intrinsically disordered proteins. Characterization of these first inter-chain interactions correlated to the aggregation kinetics will provide fundamental insight into the mechanism of amyloid formation.