Figure 3: A model incorporating a structural transition explains the effects of NaCl on aggregation kinetics.

(a) Experimental k_gr as a function of insulin concentration obtained from normalized traces at NaCl concentrations of 0 M (black squares), 0.1 M (red circles), 0.24 M (blue triangles), 0.34 M (dark cyan diamonds) and 0.49 M (pink stars). (b) Simulated data obtained by varying the elongation rate and the threshold for fragmentation cutoff. Parameters used in the simulations were CFC=0.4 mg ml⁻¹, k₊=5 × 10⁴ M⁻¹ s⁻¹ (black squares); CFC=0.4 mg ml⁻¹, k₊=10⁶ M⁻¹ s⁻¹ (red circles); CFC=0.2 mg ml⁻¹, k₊=10⁶ M⁻¹ s⁻¹ (blue triangles); CFC=0.1 mg ml⁻¹, k₊=10⁶ M⁻¹ s⁻¹ (dark cyan diamonds); and CFC=0.05 mg ml⁻¹, k₊=10⁶ M⁻¹ s⁻¹ (pink stars). For all simulations k_f=3 × 10⁻⁸ s⁻¹. (c) τ_lag as a function of insulin concentration. The data are fit with same function as Fig. 1(a) resulting in scaling exponents of γ=−0.27±0.01 (0.1 M NaCl, circles), γ=−0.56±0.05 (0.24 M NaCl, triangles), γ=−0.65±0.04 (0.34 M NaCl, diamonds), γ=−0.75±0.06 (0.49 M NaCl, stars). (d) τ_lag as a function of protein concentration obtained from simulations employing k₊=10⁶ M⁻¹ s⁻¹and k_f=3 × 10⁻⁸ s⁻¹. The scaling exponents are −0.43±0.01 (circles), −0.47±0.02 (triangles), −0.57±0.01 (diamonds), and −0.64±0.01 (stars) when the CFC is 0.4, 0.2, 0.1 and 0.05 mg ml⁻¹, respectively. Experimental and simulation data points show mean±s.d.