Structural studies on the interaction of lysozyme with dextran sulfate

The complexation between hen egg white lysozyme (Lys) and high molecular weight dextran sulfate sodium salt (DSS) was investigated by means of dynamic light scattering (DLS), phase analysis, optical microscopy and UV–vis absorption measurements at different pH and univalent electrolyte concentrations. The specific pH values where soluble complex formation is initiated (pHc) and where phase separation occurs (pHϕ) were strongly dependent on the ionic strength (I), that suggest that complexation is governed by electrostatic interaction. The effect of I on complexation has nonmonotonic character displaying maximum in complex formation at I equal 0.18–0.20. The solution behavior, structure, effective charge of the formed complexes, protein structure within the complex proved to be dependent on the pH, and the [An−]/[Cat+] charge ratio. Complexation in dilute solutions leads to spectacular stabilization of lysozyme within the complexes against thermal aggregation, whereas in semidiluted solutions its results in a considerable decrease (20°) in the temperature of denaturation, suggesting that DSS has a higher affinity for the unfolded state than the native state of lysozyme.