Tunable photophysical properties, conformation and function of nanosized protein–gold constructs

Abstract

Protein-stabilized gold nanoconstructs are widely studied due to their potential applications in biosensing, drug and gene delivery, and bioimaging. While a number of studies have focused on the novel properties of such materials emanating from the gold, there has been little focus on how the protein shell is affected by nanocluster formation with respect to conformation, stability and function. Herein, we show the synthesis of protein-stabilized gold nanoconstructs varying in size from small clusters (~8 Au atoms) dispersed within proteins to nanoparticles stabilized by multiple proteins by varying the concentration of gold precursor and reducing agent. Proteins used were bovine serum albumin (BSA), bovine a-lactalbumin (BLA) and lysozyme (LYZ). Photophysical properties of the gold nanostructures were monitored using UVvis and fluorescence measurements, revealing that the gold constructs can be tuned from luminescent clusters to nanoparticles displaying localized surface plasmon resonance (LSPR). Conformational changes of the protein following conjugation to gold nanostructures were studied using steady-state and timeresolved Trp fluorescence measurements and circular dichroism. The degree of conformational perturbation varied greatly between the proteins used, with BLA being the most tunable in terms of gradual unfolding, whereas the conformational stability of LYZ was very sensitive to the reducing agent used. To assess the impact of the gold nanostructures as well as the reducing agent on protein function, the LYZ-gold nanoconstructs were subjected to an activity test by degradation of Micrococcus lysodeikticus cell walls, revealing that the activity of the LYZ-Au constructs was retained and tunable, albeit at attenuated levels.

Self-assembly and characterization of transferrin–gold nanoconstructs and their interaction with bio-interfaces

“…In samples where only AuNCs are present, the AuNCs can be detected with fluorescence spectroscopy. [15][16][17] While the LSPR feature is prominent in the Tf-AuXH system, the band observed for Tf-AuINT has lower absorbance and occur at shorter wavelengths, indicating smaller AuNPs. 16 When AuNPs and AuNCs are in close proximity, the AuNPs can quench the emitted fluorescence from AuNCs.…”

“…16 When AuNPs and AuNCs are in close proximity, the AuNPs can quench the emitted fluorescence from AuNCs. In samples where only AuNCs are present, the AuNCs can be detected with fluorescence spectroscopy.…”

“…16 When AuNPs and AuNCs are in close proximity, the AuNPs can quench the emitted fluorescence from AuNCs. [15][16][17] Steady-state emission spectra of the Tf-AuNCs upon excitation at 370 nm are shown in Figure 1b. UV-visible spectra of the different Tf-AuNCs studied here, as well as the reference systems (Tf only and Tf treated with NaBH 4 ), are shown in Figure 1a.…”

“…From the results shown in Table 2, neither the lifetimes nor the associated populations are significantly affected by the addition of NaBH 4 . 15,16 The biggest change in the average lifetime was calculated for Tf-AuINT. For the Tf-AuXL system, there is a minor decrease in the average lifetime compared to the native protein.…”

Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold

“…Along with monolayer protected clusters, analogous systems with macromolecular protection, especially in protein templates, have also been made. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Bovine serum albumin (BSA) [29][30][31][32][33][34][35][36] , lactoferrin (Lf) 37,38 , lysozyme (Lyz) [39][40][41][42][43][44] and some other proteins like insulin 45 are used for these kind of studies, among which BSA is most thoroughly studied.…”