Figure 4.

Conformational transition of αSyn monomers induced by Ca²⁺. (A) Kratky plots of αSyn (200 μM) in the absence and presence of 50-equivalent Ca²⁺ (10 mM). (B) R_g values obtained by the Guinier analysis of SAXS scattering curves. (C) ESI-mass spectra of αSyn (20 μM) in the + 8 charge state with increasing Ca²⁺ concentration. The residual Ca²⁺ concentration of the αSyn sample without CaCl₂ (bottom) was ~30 μM and all Ca²⁺ concentrations were the sum of the residual Ca²⁺ and added CaCl₂. In the mass spectra, Ca²⁺-unbound and bound αSyn were marked with empty circles and filled circles, respectively. (D) IM-MS spectra of αSyn in the + 8 charge state with increasing number (n) of bound Ca²⁺ ions ([αSyn + nCa + (8–2n)H]⁸⁺). (E) R_g distribution of the structural ensemble (50 structures) obtained using EOM and some representative structures of the ensemble with the R_g values. Residues that are shown in blue, yellow, and red indicate the N-terminal, NAC, and C-terminal regions, respectively.