Size-selective recognition of gold nanoparticles by a molecular chaperone

Molecular chaperone prefoldin-assisted biosynthesis of gold nanoparticles with improved size distribution and dispersion

Here we report a novel aspect of molecular chaperone prefoldin (PFD) as a biomaterial in the biocatalytic synthesis of gold nanoparticles (AuNPs) using glycerol dehydrogenase (GLD). We found that PFD could inhibit the aggregation of AuNPs during the biosynthesis, leading to the formation of AuNPs with controlled size distribution.

Prefoldins in Archaea

Molecular chaperones promote the correct folding of proteins in aggregation-prone cellular environments by stabilizing nascent polypeptide chains and providing appropriate folding conditions. Prefoldins (PFDs) are molecular chaperones found in archaea and eukaryotes, generally characterized by a unique jellyfish-like hexameric structure consisting of a rigid beta-barrel backbone with protruding flexible coiled-coils. Unlike eukaryotic PFDs that mainly interact with cytoskeletal components, archaeal PFDs can stabilize a wide range of substrates; such versatility reflects PFD's role as a key element in archaeal chaperone systems, which often lack general nascent-chain binding chaperone components such as Hsp70. While archaeal PFDs mainly exist as hexameric complexes, their structural diversity ranges from tetramers to filamentous oligomers. PFDs bind and stabilize nonnative proteins using varying numbers of coiled-coils, and subsequently transfer the substrate to a group II chaperonin (CPN) for refolding. The distinct structure and specific function of archaeal PFDs have been exploited for a broad range of applications in biotechnology; furthermore, a filament-forming variant of PFD has been used to fabricate nanoscale architectures of defined shapes, demonstrating archaeal PFDs' potential applicability in nanotechnology.

Assembly of Multicomponent Protein Filaments Using Engineered Subunit Interfaces

Exploiting the ability of proteins to self-assemble into architectural templates may provide novel routes for the positioning of functional molecules in nanotechnology. Here we report the engineering of multicomponent protein templates composed of distinct monomers that assemble in repeating orders into a dynamic functional structure. This was achieved by redesigning the protein-protein interfaces of a molecular chaperone with helical sequences to create unique subunits that assemble through orthogonal coiled-coils into filaments up to several hundred nanometers in length. Subsequently, it was demonstrated that functional proteins could be fused to the subunits to achieve ordered alignment along filaments. Importantly, the multicomponent filaments had molecular chaperone activity and could prevent other proteins from thermal-induced aggregation, a potentially useful property for the scaffolding of enzymes. The design in this work is presented as proof-of-concept for the creation of modular templates that could potentially be used to position functional molecules, stabilize other proteins such as enzymes, and enable controlled assembly of nanostructures with unique topologies.

Sonochemical synthesis of gold nanoparticles by using high intensity focused ultrasound

The sonochemical synthesis of gold nanoparticles (GNPs) with different shapes and size distributions by using high-intensity focused ultrasound (HIFU) operating at 463 kHz is reported. GNP formation proceeds through the reduction of Au(3+) to Au(0) by radicals generated by acoustic cavitation. TEM images reveal that GNPs show irregular shapes at 30 W, are primarily icosahedral at 50 W and form a significant amount of nanorods at 70 W. The size of GNPs decreases with increasing acoustic power with a narrower size distribution. Sonochemiluminescence images help in the understanding of the effect of HIFU in controlling the size and shapes of GNPs. The number of radicals that form and the mechanical forces that are generated control the shape and size of the GNPs. UV/Vis spectra and TEM images are used to propose a possible mechanism for the observed effects. The results presented demonstrate, for the first time, that the HIFU system can be used to synthesise size- and shape-controlled metal nanoparticles.

Detection of DNA induced gold nanoparticle aggregation with dark field imaging

Dark field imaging was employed to visualize and quantify complementary DNA-induced gold nanoparticle aggregation at the single-particle level, with a detection limit of 100 fM DNA, which allows the highly sensitive detection of single nucleotide polymorphisms (SNPs). Results suggested that the aggregation process is consistent with the cluster-cluster model.

Naked-eye detection of amyloid aggregates using gold nanoparticles modified with amyloid beta antibody

We developed a rapid method for estimating the amyloid beta (Aβ)-conformation state related with Alzheimer's disease. We prepared gold nanoparticle (AuNP)-Aβ antibody conjugates treated with bovine serum albumin to stabilize their dispersibility in a buffer. The prepared AuNPs were precipitated in the presence of Aβ aggregates, such as oligomers and fibrils. Aβ monomers did not precipitate AuNPs. The formation of AuNP precipitates by Aβ aggregates could be confirmed by the naked eye within 1 h.