Solvent‐induced collapse of α‐synuclein and acid‐denatured cytochrome c

The effects of solution conditions on protein collapse were studied by measuring the hydrodynamic radii of two unfolded proteins, α‐synuclein and acid‐denatured ferricytochrome c, in dilute solution and in 1 M glucose. The radius of α‐synuclein in dilute solution is less than that predicted for a highly denatured state, and adding 1 M glucose causes further collapse. Circular dichroic data show that α‐synuclein lacks organized structure in both dilute solution and 1 M glucose. On the other hand, the radius of acid‐denatured cytochrome c in dilute solution is consistent with that of a highly denatured state, and 1 M glucose induces collapse to the size and structure of native cytochrome c. Taken together, these data show that α‐synuclein, a natively unfolded protein, is collapsed even in dilute solution, but lacks structure.