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Revisiting the conformational state of albumin conjugated to gold nanoclusters: A self-assembly pathway to giant superstructures unraveled.

ABSTRACT: Bovine serum albumin (BSA) is often employed as a proteinaceous component for synthesis of luminescent protein-stabilized gold nanoclusters (AuNC): intriguing systems with many potential applications. Typically, the formation of BSA-AuNC conjugate occurs under strongly alkaline conditions. Due to the sheer complexity of intertwined chemical and structural transitions taking place upon BSA-AuNC formation, the state of albumin enveloping AuNCs remains poorly characterized. Here, we study the conformational properties of BSA bound to AuNCs using an array of biophysical tools including vibrational spectroscopy, circular dichroism, fluorescence spectroscopy and trypsin digestion. The alkaline conditions of BSA-AuNC self-assembly appear to be primary responsible for the profound irreversible disruption of tertiary contacts, partial unfolding of native ?-helices, hydrolysis of disulfide bonds and the protein becoming vulnerable to trypsin digestion. Further unfolding of BSA-AuNC by guanidinium hydrochloride (GdnHCl) is fully reversible equally in terms of albumin's secondary structure and conjugate's luminescent properties. This suggests that binding to AuNCs traps the albumin molecule in a state that is both partly disordered and refractory to irreversible misfolding. Indeed, when BSA-AuNC is subjected to conditions favoring self-association of BSA into amyloid-like fibrils, the buildup of non-native ?-sheet conformation is less pronounced than in a control experiment with unmodified BSA. Unexpectedly, BSA-AuNC reveals a tendency to self-assemble into giant twisted superstructures of micrometer lengths detectable with transmission electron microscopy (TEM), a property absent in unmodified BSA. The process is accompanied by ordering of bound AuNCs into elongated streaks and simultaneous decrease in fluorescence intensity. The newly discovered self-association pathway appears to be specifically accessible to protein molecules with a certain restriction on structural dynamics which in the case of BSA-AuNC arises from binding to metal nanoclusters. Our results have been discussed in the context of mechanisms of protein misfolding and applications of BSA-AuNC.

SUBMITTER: Kluz M

PROVIDER: S-EPMC6597083 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Revisiting the conformational state of albumin conjugated to gold nanoclusters: A self-assembly pathway to giant superstructures unraveled.

Kluz Michał M Nieznańska Hanna H Dec Robert R Dzięcielewski Igor I Niżyński Bartosz B Ścibisz Grzegorz G Puławski Wojciech W Staszczak Grzegorz G Klein Ewelina E Smalc-Koziorowska Julita J Dzwolak Wojciech W

PloS one 20190627 6

Bovine serum albumin (BSA) is often employed as a proteinaceous component for synthesis of luminescent protein-stabilized gold nanoclusters (AuNC): intriguing systems with many potential applications. Typically, the formation of BSA-AuNC conjugate occurs under strongly alkaline conditions. Due to the sheer complexity of intertwined chemical and structural transitions taking place upon BSA-AuNC formation, the state of albumin enveloping AuNCs remains poorly characterized. Here, we study the confo ...[more]

PMID: 31247048

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Project description:Photon-to-matter chirality transfer offers both simplicity and universality to chiral synthesis, but its efficiency is typically low for organic compounds. Besides the fundamental importance of this process relevant for understanding the origin of homochirality on Earth, new pathways for imposing chiral bias during chemical process are essential for a variety of technologies from medicine to informatics. The strong optical activity of inorganic nanoparticles (NPs) affords photosynthetic routes to chiral superstructures using circularly polarized photons. Although plasmonic NPs are promising candidates for such synthetic routes due to the strong rotatory power of highly delocalized plasmonic states (Ma et al. Chem. Rev. 2017, 117 (12), 8041), realization of light-driven synthesis of chiral nanostructures has been more challenging for plasmonic NPs than for the semiconductor due to the short lifetime of the plasmonic states. Here we show that illumination of gold salt solutions with circularly polarized light induces the formation of NPs and their subsequent assembly into chiral nanostructures 10-15 nm in diameter. Despite their seemingly irregular shape, the resulting nanocolloids showed circular dichroism (CD) spectra with opposite polarity after exposure to photons with left and right circular polarization. The sign and spectral position of the CD peaks of illuminated dispersions matched those calculated for nanostructures with complex geometry identified from electron tomography images. Quantification of the complex shapes of NP assemblies using chirality measures revealed a direct correlation with the experimental spectra. The light-driven assembly of chiral nanostructures originates from the asymmetric displacement of NPs in dynamic assemblies by plasmonic fields followed by particle-to-particle attachment. The ability of gold NPs to "lock" the chirality of the incident photons in assembled nanostructures can be used to create a variety of chiral nanomaterials with plasmonic resonances.

Dataset Information

Revisiting the conformational state of albumin conjugated to gold nanoclusters: A self-assembly pathway to giant superstructures unraveled.

Publications

Revisiting the conformational state of albumin conjugated to gold nanoclusters: A self-assembly pathway to giant superstructures unraveled.

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