Abstract
α-synuclein (α-syn) is the main component of Lewy bodies, which are neuropathological hallmarks of patients with Parkinson’s disease. As it has been controversial whether human α-syn from erythrocytes exists as a tetramer under physiological conditions, we tried solving this issue by the small-angle X-ray solution scattering method. Under two different conditions (high ionic strength with a Tris buffer and low ionic strength with an ammonium acetate buffer), no evidence was found for the presence of tetramer. When comparing erythrocyte and recombinant α-syn molecules, we found no significant difference of the molecular weight and the secondary structure although the buffer conditions strongly affect the radius of gyration of the protein. The results indicate that, even though a stable tetramer may not be formed, conformation of α-syn depends much on its environment, which may be the reason for its tendency to aggregate in cells.
Highlights
While the spectrum of α-syn purified from human RBC (RBC α-syn) showed a typical random coil profile in the AA buffer (Fig. 1c), it suggested the presence of secondary structure, difficult to analyze in detail, in the Tris buffer (Fig. 1d)
The SAXS measurements were made in the buffer condition in which they found tetramers
At the concentration commonly used for the SAXS measurements, we found that the protein was monomeric
Summary
The Rg value of N-terminally acetylated recombinant α-syn (NAc) was 4.04 ± 0.22 nm (n = 4) and 3.09 ± 0.18 nm (n = 2) in the Tris and AA buffers, respectively. In the static SAXS experiment, small-angle scattering curves from recombinant WT α-syn in the Tris buffer had only a limited region that can be used for the Guinier analysis (Fig. 2c,d).
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