Counter ion induced irreversible denaturation of hen egg white lysozyme upon electrostatic interaction with iron oxide nanoparticles: A predicted model

The effects of electrostatic interaction between the hen egg white lysozyme (HEWL) and the functionalized iron oxide nanoparticles (IONPs) have been investigated using several techniques, e.g., CD, DSC, ζ-potential, UV–visible spectroscopy, DLS, TEM. Nanoparticles (IONPs) were functionalized with three hydrophilic ligands, viz., poly(ethylene glycol) (PEG), trisodium citrate (TSC) and sodium triphosphate (STP); where both TSC and STP contain Na+ counter ions. It has been observed that the secondary structure of HEWL was not affected by PEG functionalized IONPs, but was partially and almost completely perturbed by TSC and STP functionalized IONPs, respectively. The perturbation of the secondary structure was irreversible. We have predicted an interaction model to explain the origin of perturbation of HEWL structure. We have also investigated the stability of nanoparticles dispersions after interaction with HEWL and used the DLVO theory to explain results.

Figure optionsDownload as PowerPoint slideHighlights
► Electrostatic interaction between the hen egg white lysozyme (HEWL) and the hydrophilic iron oxide nanoparticles (IONPs).
► First report on the application of DSC technique for the nanoparticle protein interaction study.
► First report on the functionalization of IONPs by sodium tripolyphosphate (STP).
► STP functionalized IONPs has denatured HEWL, though pure STP is used to preserve protein structure.
► Phenomenological interaction model to explain the denaturation of HEWL.
► DLVO calculation for understanding the dispersion stability after protein–nanoparticles interaction.