Effect of L-Arginine Modified Magnetic Nanoparticles (RMNPs) on Lysozyme in the Presence or Absence of Urea

L-Arginine (Arg or R) is a non-toxigenic, metabolically versatile and conditionally essential amino acid. Single-pot synthesis of Arg modified magnetic nanoparticles (RMNPs) was achieved using magnetite nanoparticles (MNPs) and binary function of Arg as a functional group and an alkali precipitator. This modification is supposed to offer several advantages to the MNPs from a bio-application viewpoint. Here, the influence of RMNPs in the structure and function of the model protein hen egg white lysozyme (HEWL) is reported. After synthesis of RMNPs, VSM, XRD, FT-IR, Zetasizer, TEM, and SEM were used to characterize the nanoparticles. The impact of RMNPs was investigated on lysozyme structure and activity during storage and in the processes of denaturation and refolding by dilution or dialysis using fluorescence, circular dichroism (CD) and UV/Vis spectroscopies. RMNPs revealed structural ordering or disordering effects on lysozyme in a RMNP:HEWL ratio dependent manner. Accordingly, a concentration ratio of threshold (CRT) was determined at 0.296. At ratios lower than the CRT the protein gained more ordered structure with increased helicity. Inversely, HEWL was increasingly unfolded and helicity was decreased at ratios higher than the CRT, rendering the protein more disordered after interaction with RMNPs. At RMNPs:HEWL concentration ratios above and even below the CRT, 6 M urea had a further disordering effect. Nevertheless, significant improvements were observed in the refolding of the protein due to dilution or dialysis, by courtesy of the RMNPs. The presented data helps to expand the thriving applications of RMNPs in biotechnology and biomedicine.