α-Synuclein Spontaneously Adopts Stable and Reversible α-Helical Structure in Water-Less Environment

A highly stable, spontaneous, and reversible α-helical-structure formation in recombinant and chemically modified α-synuclein protein is demonstrated for the first time in a water-less (1.5 % w/w H₂ O) polymer surfactant environment. Using a combination of circular dichroism and ATR-FTIR spectroscopy, we show that whilst native α-synuclein in aqueous solution shows a predominant unordered conformation (≈64 %), mixing with polyethylene glycol based anionic polymer surfactant (PS) and removing water reveals a 25 % unordered, 25 % α-helical, and 27 % β-sheet structure. Interestingly, bioconjugation of native α-synuclein with a diamine molecule, to increase the positive charge on the protein chain, and subsequent electrostatic coupling with the PS forms a conjugate with a retained unordered structure. Removal of water from this system provides a highly stable α-helical (≈74 %) water-less liquid system. Surprisingly, the α-helical-to-unordered state transition is completely reversible and is achieved at ≈25-30 w/w% of water in the system. Moreover, the α-helix shows an extraordinary temporal stability (>6 months) in a waterless environment.