Enhanced activity of lysozyme-AgNP conjugate with synergic antibacterial effect without damaging the catalytic site of lysozyme

CONTEXT: The conjugation of silver nanoparticles (AgNPs) with biomolecules such as oligosaccharides, DNA, proteins has attracted great attention of scientists recently. OBJECTIVE: In this study, lysozyme-AgNP conjugates were evaluated for its synergic antimicrobial effect. MATERIALS AND METHODS: AgNPs were synthesized and characterized using UV-Visible, X-ray diffraction analysis (XRD) and atomic force microscopy (AFM). AgNP (0-1 mM) was interacted with lysozyme for multi-spectrophotometric studies. Lysozyme was immobilized on AgNP at different ratios and the resulting nano-bio-conjugate was tested against Escherichia coli for potent synergic antibacterial effects. RESULTS AND DISCUSSION: A surface plasmon peak at 420 nm confirmed the presence of AgNPs and spherical to oval-shaped AgNPs were observed by AFM. The particle size was calculated to be 25 nm by XRD analysis. The maximum immobilization efficiency (98%) was achieved at 0.01:1 ratio of enzyme:AgNP. UV-Visible and fluorescence spectral studies revealed the binding of AgNPs to lysozyme by the formation of ground-state complex and the binding parameters were calculated. Circular dichroism studies confirmed decrease by 11% in the α-helical and 29.32% in β-sheets of lysozyme upon AgNP interaction. FTIR spectra revealed the binding of AgNP through thiol (-SH) linkages of lysozyme. Our results showed that the antimicrobial activity of lysozyme-AgNP conjugate was enhanced up to 86% decrease in the cell growth. CONCLUSION: In summary, the immobilization of lysozyme on AgNP has yielded a nano-bio-conjugate with synergistic antibacterial properties.