Jones-Ray effect on the organization of lysozyme in the presence of NaNO3 at an air/water interface: is it a cause or consequence?

Abstract

The study reports on the anomalous aggregation and enhanced viscosity of lysozyme (Lyz) in the presence of low concentrations of sodium nitrate at an air/buffer interface. For salt concentrations of about 10 mM of NaNO₃, the interactions seem to be electrostatic in origin possibly due to the anisotropy of charge distribution on the protein and its correlation with high-complementarity non-electrostatic interactions resulting in a sudden increase in viscosity values. In the presence of low concentrations of the electrolyte, a thick viscoelastic protein film is created due to local amorphous aggregation, while native Lyz adsorbs in a fragile monolayer film without changing its secondary structural features. On increasing concentration beyond 10 mM, the protein behaves almost like a pure buffer without showing any surface activity or aggregation and is highly stable at the interface. For the first time, the rheological changes here confirm the Jones-Ray effect due to the synergy between NaNO₃ (∼10 mM) and the protein whereas earlier reports on this effect have dealt only with pure electrolyte–water interactions. Our experimental studies indicate that with the appropriate choice of solution conditions and specific electrolyte concentration, one can either drive the protein to form amorphous aggregates which can result in protein crystallization or enhance protein stability for long time periods by preventing aggregation through self-association.