Solvent Isotope Effects in Protein Adsorption and Crystallization

We investigate the effects of D2O (heavy water) versus H2O (normal water) on protein adsorption and crystallization using human serum albumin (HSA) as a model protein in the presence of lanthanum chloride (LaCl3). We use optical microscopy to investigate the crystallization, quartz crystal microbalance with dissipation monitoring (QCM-D) to follow protein adsorption, and dynamic light scattering (DLS) to study cluster formation prior to crystallization. The results show that D2O induces a higher crystallization density (number of crystals) and the formation of larger crystals; furthermore, D2O significantly slows down the crystallization kinetics. HSA adsorbs more mass at the surface when the solvent is heavy water, which contributes to the higher crystallization density. Additionally, we find that in heavy water, larger clusters are stabilized prior to crystal growth, which delays the kinetics of crystallization. We speculate that this is due to the modified effective solvent interactions.