Time dependence of aggregation in crystallizing lysozyme solutions probed using NMR self-diffusion measurements

The time dependence of aggregation in supersaturated lysozyme solutions was studied using pulsed-gradient spin-echo NMR diffusion measurements as a fu nction of lysozyme concentration at pH 6.0 and 298 K in the presence of 0.5 M NaCl. The measurements provide estimates of the weight-averaged diffusio n coefficient of the monomeric to intermediate molecular weight lysozyme sp ecies present in the solution (very large aggregates and crystals are exclu ded from the average due to the NMR relaxation-weighting effects inherent i n the method). The results show that the average molecular weight of the va rious lysozyme aggregates changed with sigmoidal kinetics and that these ki netics were strongly influenced by the initial lysozyme concentration. The visualization of the time dependence of the protein aggregation afforded by this method provides a deeper understanding of how the crystallizing condi tions (especially the initial protein concentration) are related to the res ulting crystals.