Structure, stability and chaperone function of Mycobacterium leprae Heat Shock Protein 18 are differentially affected upon interaction with gold and silver nanoparticles.

Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) have several biomedical applications. However, the effective usage of these two nanoparticles is impeded due to limited understanding of their interaction with proteins including small heat shock proteins (sHSPs). Specifically, no evidences of interaction of these two nanoparticles with HSP18 (an antigenic protein) which is an important factor for the growth and survival of M. leprae (the causative organism of leprosy) are available in the literature. Here, we report for the first time evidences of "HSP18-AuNPs/AgNPs interaction" and its impact on the structure and chaperone function of HSP18. Interaction of citrate-capped AuNPs/AgNPs (~20 nm diameter) to HSP18 alters the secondary and tertiary structure of HSP18 in a distinctly opposite manner; while "HSP18-AuNPs interaction" leads to oligomeric association, "HSP18-AgNPs interaction" results in oligomeric dissociation of the protein. Surface hydrophobicity, thermal stability, chaperone function of HSP18 and survival of thermally stressed E. coli harbouring HSP18 are enhanced upon AuNPs interaction, while all of them are reduced upon interaction with AgNPs. Altogether, our study reveals that HSP18 is an important drug target in leprosy and its chaperone function may possibly plays a vital role in the growth and survival of M. leprae pathogen in infected hosts.