Understanding Protein Structure Deformation on the Surface of Gold Nanoparticles of Varying Size

Abstract

Gold nanoparticles (AuNPs) have been of recent interest due to their unique optical properties and their biocompatibility. Biomolecules spontaneously adsorb to their surface, a trait that could potentially be exploited for drug targeting. Currently, it is unclear whether protein–AuNP interactions at the nanoparticle surface are dependent on nanoparticle size. In this work, we investigate whether varying surface curvature can induce protein unfolding and multilayer binding in citrate-coated AuNPs of various sizes. A recently developed NMR-based approach was utilized to determine the adsorption capacity, and protein NMR spectra were compared to determine whether nanoparticle size influences protein interactions at the surface. In addition, transmission electron microscopy (TEM) and dynamic light scattering (DLS) were employed to corroborate the NMR studies. Over a broad range of AuNP sizes (14–86 nm), we show that adsorption capacity can be predicted by assuming that proteins are compact and globular on the nanoparticle surface. Additionally, roughly one layer of proteins is adsorbed regardless of AuNP size. Our results hold for two proteins of significantly different sizes, GB3 (6 kDa) and bovine carbonic anhydrase (BCA, 29 kDa). However, the unstable drkN SH3 domain (ΔḠ0 ≈ 0, 7 kDa) does not appear to follow the same trend seen for stable, globular proteins. This observation suggests that unstable proteins can deform significantly when bound to AuNP surfaces. Taken together, the results of this work can be used to improve our knowledge of the mechanism of protein–AuNP interactions to optimize their use in the biomedical field.

Protein Interactions with Nanoparticle Surfaces: Highlighting Solution NMR Techniques

“…Woods et al . studied the monolayer formation of BCA and GB3 on AuNP using DLS . The size increment when both proteins adsorbed to AuNP was similar to the values observed by TEM and the values predicted by the native protein structure .…”

“…studied the monolayer formation of BCA and GB3 on AuNP using DLS . The size increment when both proteins adsorbed to AuNP was similar to the values observed by TEM and the values predicted by the native protein structure . DLS is a nonperturbative, fast, and accurate method, but the disadvantage is the need of a dust free and dilute sample that has a monodisperse population.…”

“…In both of these cases, binding is in very slow exchange, allowing the quantification of adsorbed protein . It would appear that, for many stable globular proteins interacting with medium size AuNPs (10–80 nm), monolayer binding on the AuNP surface gives rise to a stable hard corona with little evidence for a dynamic, soft corona. Unstable, non‐globular proteins and intrinsically disordered proteins (IDPs) behave differently, suggesting that these proteins have altered conformations on the AuNP surface.…”

Geometry-induced protein reorientation on the spikes of plasmonic gold nanostars

“…[12][13][14][15][16][17] A recent report measured binding of GB3 and BCA proteins onto spherical gold nanoparticle surfaces with varied radius of curvature and showed, using NMR, that the adsorbed protein structure is independent of curvature for these proteins. 18 However, to our knowledge it is unknown how protein binding and structure compare on the surface of star-shaped (AuStr) and spherical gold nanostructures. In particular, the differences in surface energy, related to the dramatic differences in local curvature are likely to inuence protein adsorption along the stem and tips of the AuStr's spikes.…”

Interaction between cyanine dye IR‐783 and polystyrene nanoparticles in solution

“…Nuclear Magnetic Resonance (NMR) is the most versatile tool for determining molecular structure. NMR is being increasingly used in recent years to examine molecules that interact noncovalently with nanoparticle surfaces . Previously, we have used Saturation‐Transfer Difference (STD) NMR to examine the binding between small molecules and the surface of polystyrene (PS) nanoparticles.…”