Multi-angle static and dynamic light scattering investigation of lysozyme association: From crystallization to liquid–liquid phase separation

The association of hen egg white lysozyme was observed using time-resolved multi-angle static and dynamic light scattering. In solutions containing 1.2 M of NaCl with a pH of 4.6 buffered by 50 mM of NaAc, and maintained at 20∘C, the apparent molecular weight MwMw, and gyration radius RgRg, of lysozyme aggregates were measured at 0.3–5-s intervals for various lysozyme concentrations from 8 to 32 mg/mL using static light scattering. At 32 mg/mL, liquid–liquid phase separation (LLPS) occurred. The (Kc/ΔR(q))1/2(Kc/ΔR(q))1/2 vs. q2q2 plot had a non-linear shape with a maximum at a particular q2q2, indicating that the aggregate size distribution was within a narrow range. This had not been observed in our previous studies of high-molecular-weight proteins. The dynamic light scattering data were consistent with those of static light scattering; i.e., CONTIN analysis showed clear bimodal (monomer and aggregate) distributions. Fractal dimension analysis of the aggregates with the protein concentration showed that the inner structure of the scatterer formed during LLPS was rigid in the final stage, which supports a two-step nucleation model.