Proline-Functionalized ZnO (Zinc Oxide) Nano-Osmolytes: Potent Catalysts for Protein Aggregation Versus Pristine ZnO

Among different classes of osmolytes, proline is known for the prevention of protein aggregation. A limited number of studies have demonstrated the effectiveness of synthesized nano-osmolytes in stabilizing protein from aggregating. Because of the unknown characteristics of nanoparticles, it is essential to comprehend the effectiveness of recently synthesized nano-osmolytes in maintaining the stability of the protein. It is known that proline is effective at high molar concentrations and non-specific to various molecular targets for its biomedical applications. To enhance its efficiency, ZnO (zinc oxide), a known biocompatible nanoparticle, is used as proline-functionalized zinc oxide (ZnOP). Synthesis of ZnO and ZnOP was performed through the sol-gel method. Our results of chemical and denaturation studies suggest that conjugated ZnOP is perturbing more on the stability of the protein as compared to the equimolar mixture of ZnO and proline. Our biophysical studies reveal that ZnOP interacts more with the hydrophobic groups of BSA (bovine serum albumin) and acts as an intercalating agent to bind more BSA molecules to form higher aggregates. ZnO behaves as a denaturing agent whereas a mixture of ZnO and proline at higher temperature promotes fibrillation of the protein. Additionally, proline at 0.2 mM is effective against the unfolding of the protein at 1 M urea concentration, whereas ZnOP is perturbing more on the stability of protein than a mixture of ZnO and proline at the same condition. We conclude that ZnO could not be used as a biocompatible nano-carrier of proline osmolyte.