Fundamental Understanding of Bio-Nano Interface of Lysozyme on Psidium guajava Polyphenol Coated Silver Nanoparticles: Mechanistic Insights into the Effect of Protein Corona on the Antibacterial Efficacy

Abstract

Recent times have witnessed revolutionary progress in the design and development of functionalized nanomaterials as promising tools for biomedicinal applications. However, the gap in the fundamental understanding of the “biological responses” of the nanomaterials after the formation of “protein-corona” when it is exposed to the body system has drawn a thin line from its discoveries to real clinical trial. In this article we have synthesized two different silver NPs capped with the polyphenols of Psidium guajava (guava) leaf extract and the other with one of its major polyphenolic groups, morin. Then, the formation of “bio-nano interface” of these synthesized AgNPs were illustrated in detail by taking the model carrier protein hen egg white lysozyme (HEWL). The formation of protein corona of HEWL on the surface of the AgNPs was revealed by the increase in the hydrodynamic size and the negative ξ-potential values as well as from the visualization of an ∼1 nm thick light gray layer of HEWL in the TEM micrographs. The binding interaction of surface adsorbed HEWL with the AgNPs was analyzed with various photophysical and molecular dynamics simulation (MD) techniques. HEWL interacted with these polyphenol-assisted AgNPs with moderate binding affinity (K_b ∼ 10⁴ M^–1) in a spontaneous manner with the structural integrity in its native conformation. Though several covalent forces are responsible for protein–NP interaction, electrostatic and hydrophobic forces of attraction played the major role in the complexation of HEWL with Guava L.-AgNPs and Morin-AgNPs, respectively. The lysozyme protein-corona on the synthesized polyphenol-assisted AgNPs altered their biological response as revealed from the reduction of antibacterial activity against pathological Gram-positive (E. faecalis) as well as Gram-negative (E. coli) bacterial strains in vitro.