Conformational changes and bioactivity of lysozyme on binding to and desorption from magnetite nanoparticles

A fundamental understanding of the conformational behaviors of lysozyme during the process of adsorption and desorption has been studied using spectrophotometric techniques, and interpreted in terms of the secondary structures in this work. FTIR data show an increase in α-helix and β-sheet content when lysozyme interaction with magnetite nanoparticles (Fe3O4 (PEG + CM-CTS) NPs) which indicates that the lysozyme would adopt a more compact conformation state. The mechanism of fluorescence quenching of lysozyme by magnetite nanoparticles is due to the formation of lysozyme–nanoparticles complex. High desorption of lysozyme from Fe3O4 (PEG + CM-CTS) NPs were achieved using phosphate buffer solution (PBS) (20 mM, pH 5.0, 0.2 M NaCl), PBS (20 mM, pH 5.0, 0.5 M NaCl) and acetic acid (0.2 M, pH 4.0) as eluents. The alterations of lysozyme secondary structure on desorption from nanoparticles were confirmed by circular dichroism and fluorescence spectroscopy. Lysozymes desorbed by PBS (20 mM, pH 5.0, 0.2 M NaCl) and PBS (20 mM, pH 5.0, 0.5 M NaCl) retain high fraction of its native structure with negligible effect on its activity, and about 92.4% and 89.5% activity were retained upon desorption from nanoparticles, however, lysozyme desorbed by acetic acid (0.2 M, pH 4.0) solution showed significant conformational changes. The stability of NPs-conjugated protein and retention of higher activity may find useful applications in biotechnology ranging from enzyme immobilization to protein purification.