Probing the Aggregation Mechanism of Gold Nanoparticles Triggered by a Globular Protein

Abstract

Gold nanoparticles (AuNPs) are advancing a number of areas. Meanwhile, the inevitable contact of AuNPs with surrounding biomolecules has been realized to “negatively” impact the nanoparticle (NP) function, biological environment, and even public health. Understanding the mechanisms of the NP–biomolecule interaction often leads to revealing the pathways toward the negative, deleterious effects. It is therefore essential to know the undesirable pathways so that these unwanted effects can be reduced by blocking or rerouting these pathways. A fundamental step to understand the interaction mechanism is to elucidate the changes in protein structure and dynamics and in NP properties upon the contact of AuNPs and protein, at the molecular level. However, it is challenging to probe these areas experimentally due to the large size and the complexity of the protein–nano interface. Here we report the use of a unique approach, electron paramagnetic resonance (EPR) spectroscopy, to probe the structure and dynamics of a model protein, T4 lysozyme (T4L), upon interaction with AuNPs. In combination with circular dichroism (CD) spectroscopy, UV–vis spectroscopy, and a protein activity assay, we found that T4L triggered the AuNPs to aggregate but remained in its native structure. Remarkably, our results also revealed the pathways of how T4L triggers AuNP aggregation, the potential applications of which were discussed. Lastly, this work demonstrated the usefulness of the EPR spectroscopy in probing the complexes formed by nanomaterials and macrobiomolecules, opening a new window to probe the nano–bio interface in the native state.

Formation of a Monolayer Protein Corona around Polystyrene Nanoparticles and Implications for Nanoparticle Agglomeration

“…At low protein concentration, only one or a few proteins weakly adhere to the NP on average, and protein–protein interactions are less likely to occur. Thus, each weakly bound protein molecule unfolds individually, and its linear polypeptide chain spreads across the surface and covers an area of several times its footprint in the folded state (Figure ) . The actual dimension of the footprint depends on the relative strength of the protein–surface interaction and the internal stability of the protein.…”

Insights on the Structure, Molecular Weight and Activity of an Antibacterial Protein–Polymer Hybrid

“…Another possibility is PEG somehow disrupts the interaction of the protein with the substrate, which changes the surface charge of the hybrid and/or blocks the access pathway of substrates. Our recent work showed that T4L was able to trigger the aggregation of small AuNPs (14 nm) due to the positive surface charge . Therefore, AuNPs are effective sensors to probe T4L charges.…”

“…The details of polymer modification and polymer‐protein conjugation are provided in the SI. The AuNPs were prepared using a known procedure with minor modifications . UV spectra were obtained with the NanoDrop UV‐vis spectrophotometer (Thermo Scientific ND‐2000 C) at the Core Biology Facility of Department of Chemistry and Biochemistry, North Dakota State University (NDSU).…”

Spin‐labeling of polymeric micelles and application in probing micelle swelling using EPR spectroscopy

“…Static Light Scattering (SLS) was conducted on a Zetasizer Nano‐ZS (Malvern ZEN 3690, Malvern Instruments). A Varian E‐109 spectrometer fitted with a cavity resonator was used for all CW EPR studies . The typical sample concentration for our CW EPR studies was ∼100 μM.…”