The biocompatible validity of amino acid ionic liquid mediated gold nanoparticles for enhanced activity and structural stability of papain.

During the past few decades, gold nanoparticles (AuNPs) have attracted a lot of attention owing to their biomedical applications, like therapeutics and drug delivery; however, the detailed biomolecular interactions and structural alteration of naturally occurring biomolecules, such as enzymes, in AuNPs remain unknown. The effects of various additives on the thermal and structural properties, and activity of proteins/enzymes have been scavenged and communicated intensively in the literature; however, the synthesis of ionic liquid (IL) mediated AuNPs solely for the purpose of enzyme activity boosting and stability modulation has not yet been reported. In the current study, we explore the role of cholinium tryptophan [CHO][Trp] and tetraethyl tryptophan [TEA][Trp]IL-mediated gold nanoparticles (AuNPs) on the activity enhancement and structural stability of papain. Our results showed that [CHO][Trp] and [TEA][Trp]IL-mediated AuNPs efficiently increased the proteolytic activity of papain, which was increased from 100 to 206% for [CHO][Trp]IL-mediated AuNPs and enhanced from 100 to 136% in [TEA][Trp]IL-mediated AuNPs. Additionally, extended differential scanning calorimetry (DSC) results showed that these AAIL-mediated AuNPs maintained the thermal stability of papain only at lower concentration. Spectroscopic studies conclude that the tryptophan (Trp) group of papain is expanded more towards the polar environment in the presence of [CHO][Trp] as compared to [CHO][Trp]IL mediated AuNPs. The far CD spectral and deconvoluted results show that the α-helical and β-turn contents of the secondary structure of papain are preserved to a large extent; however, disruption in the β-sheet has been observed for both AAIL-mediated AuNPs. Dynamic light scattering (DLS), zeta potential and transmission electron microscopy (TEM) results illustrate the distinct interactive behavior of papain for both types of AAIL-mediated AuNPs. The immobilization of papain is higher on [CHO][Trp]AuNPs compared to [TEA][Trp]AuNPs and papain surrounds [CHO][Trp]AuNPs on all sides, which is lacking in [TEA][Trp]AuNPs.