Protein-Nanomaterial Interactions: Structural And Dynamic Aspects
Owing to their unique properties, the noble metallic nanoparticles and graphenic nanomaterials find their applications in diverse fields of science. Particularly in the field of biomedicine, nanomaterials are being used in drug delivery, tumor targeting, bio-sensing, tissue engineering and photo thermal therapy. The accidental or the intentional exposure of human body towards these nanomaterials paves their way into the body. But at the same time, the knowledge about the exposure risks and the biocompatibility of these nanomaterials remains largely unknown. Some of the studies have found that the nanomaterials show adverse effects towards the biological systems under in vitro and in vivo conditions. When these nanomaterials come in contact with biomolecules, such as peptides and proteins, layers of biomolecules cover their surfaces, leading to the formation of a dynamic and competitive protein corona. The formation of protein corona has the potential to affect the properties of both the nanoparticles (e.g., cellular uptake, accumulation, degradation and clearance from the body) and the protein adsorbed on the surface (e.g., protein conformation and function). Hence, unexpected biological responses and toxicity may be induced. It therefore becomes important to probe the nature of interactions of biomolecules at their individual residual level with nanomaterials. Depending upon the surface charges of both; the nanomaterials and the proteins, there may either be strong and irreversible or weaker and reversible interactions between proteins and nanomaterials involving electrostatic or covalent interactions. Thus, the understanding of such protein-nanomaterial interactions can be exploited for the generation of the safe and biocompatible nanomaterials with optimized surface properties in a biological milieu. The main aim of our work is to probe into the residual level conformational changes in the proteins in presence of nanomaterials and the dynamic aspects of such interactions. Using two-dimensional NMR spectroscopy in combination with other biophysical techniques we report that the citrate capped silver nanoparticles (AgNPs) have the ability to stabilize an intrinsically disordered protein (IDP) against the proteolysis by masking the proteolytic prone sites on the protein thereby rendering it stable for a month against proteolytic degradation. Our studies reveal the extent and nature of residue-specific interactions of the IDP with AgNPs. This study will be helpful in designing the appropriate nanoparticles targeting IDPs and for storage, stabilization and delivery of IDPs into cells in a stable form. Our other findings show that human ubiquitin (a globular protein) interacts electrostatically with the different graphene oxides (GOs) having varying amounts of defects, oxidation levels, and surface chemistry. The protein undergoes a dynamic and reversible exchange (fast exchange regime) on the surface of the GOs. The interaction does not involve any change in the secondary structure of the protein. We further investigated the aggregation tendency of human alpha synuclein in presence of the gold nanoparticles and graphene oxide. Our results show that the gold nanoparticles act as the catalysts in the aggregation process of human alpha synuclein while as the GO shows inhibitory actions on the aggregation tendency of the same protein under the similar conditions by effecting the main phases (nucleation and growth) amyloid kinetics. Furthermore, we show here that the protein-nanoparticle interaction is largely electrostatic in nature and the binding affinity of the human alpha synuclein for the citrate capped gold nanoparticles is lower than that of the GO. Hence the nature of interactions and the binding affinity of the protein towards the nanomaterials decide the path of the protein aggregation (enhanced aggregation or inhibited aggregation). Our results help in exploring the mechanism of protein aggregation at the individual residue level and the respective catalytic and inhibitory effects of gold nanoparticles and GO in protein aggregation and hence will prove to be fruitful in devising the potential therapeutic reagents against Parkinson’s and other neurodegeneratory diseases.