characterization-ph-dependent-reversible-self-assembly-amyloid-beta-1

Characterization of pH-Dependent Reversible Self-Assembly of Amyloid Beta 1-40-Coated Gold Colloids

The characterization of A&#946;1-40 coated over the nano-gold colloidal particle surfaces was conducted using surface plasmon resonance (SPR) spectroscopy ...

State University of New York Geneseo College

The absorption spectrum of the amyloid beta 1-40 peptide (Abeta(1-40)) conjugated to gold colloidal suspension of 15, 20, 30, and 40 nm size were examined under temperature ranging from 5 to 50 degrees C. As the pH was externally altered repetitively between pH 4 and 10, Abeta(1-40)-coated 20 nm gold colloid nanoparticles exhibited a reversible color change at the entire temperature range tested in this study except for 5 +/- 0.2 degrees C. This reversible change may be due to the fact that hydrophilic Abeta(1-40) evolves between a three-dimensional network containing mainly beta-sheet and alpha-helices, and an intermediate of this process implies a reversible step reported as initiation of the fibrillogenesis in Alzheimer's disease. When other nanosize particles were investigated, Abeta(1-40)-coated 30 and 40 nm colloids exhibited the reversible color change when temperature was lowered to 18 +/- 0.2 and 6 +/- 0.2 degrees C, respectively. This specific and unique size and temperature dependence in reversible color change strongly suggests that the noncovalent intrinsic intermolecular potential formed between the nanocolloidal surface and each Abeta(1-40) monomer conjugated at the surface drives the process.

Temperature dependence of conjugation of amyloid beta protein on the surfaces of gold colloidal nanoparticles.

The adsorption of amyloidogenic peptides, amyloid beta 1-40 (Aβ), alpha-synuclein (α-syn), and beta 2 microglobulin (β2m), was attempted over the surface of nano-gold colloidal particles, ranging from d = 10 to 100 nm in diameter (). The spectroscopic inspection between pH 2 and pH 12 successfully extracted the critical pH point (pH) at which the color change of the amyloidogenic peptide-coated nano-gold colloids occurred due to aggregation of the nano-gold colloids. The change in surface property caused by the degree of peptide coverage was hypothesized to reflect the ΔpH, which is the difference in pH between bare gold colloids and peptide coated gold colloids. The coverage ratio (Θ) for all amyloidogenic peptides over gold colloid of different sizes was extracted by assuming Θ = 0 at ΔpH = 0. Remarkably, Θ was found to have a nano-gold colloidal size dependence, however, this nano-size dependence was not simply correlated with . The geometric analysis and simulation of reproducing Θ was conducted by assuming a prolate shape of all amyloidogenic peptides. The simulation concluded that a spiking-out orientation of a prolate was required in order to reproduce the extracted Θ. The involvement of a secondary layer was suggested; this secondary layer was considered to be due to the networking of the peptides. An extracted average distance of networking between adjacent gold colloids supports the binding of peptides as if they are "entangled" and enclosed in an interfacial distance that was found to be approximately 2 nm. The complex nano-size dependence of Θ was explained by available spacing between adjacent prolates. When the secondary layer was formed, Aβ and α-syn possessed a higher affinity to a partially negative nano-gold colloidal surface. However, β2m peptides tend to interact with each other. This difference was explained by the difference in partial charge distribution over a monomer. Both Aβ and α-syn are considered to have a partial charge (especially δ+) distribution centering around the prolate axis. The β2m, however, possesses a distorted charge distribution. For a lower Θ (i.e., Θ <0.5), a prolate was assumed to conduct a gyration motion, maintaining the spiking-out orientation to fill in the unoccupied space with a tilting angle ranging between 5° and 58° depending on the nano-scale and peptide coated to the gold colloid.

Examination of Adsorption Orientation of Amyloidogenic Peptides Over Nano-Gold Colloidal Particle Surfaces.

The affinity of the SARS-CoV-2 spike protein (S protein) to gold nano-particles was examined through spectral shifts of SPR (Surface Plasmon Resonance) band. Gold nano-colloidal particles are sensitive to the conformational change of the protein adsorbed over the particles' surface. As the pH value was gradually lowered from approximately neutral pH to an acidic pH ( pH 2), all mixtures of S protein with the gold colloids ≥30 nm in diameter exhibited a drastic red-shift of the average SPR band peak at one pH value more than that observed for bare gold colloids. The surface coverage fraction (Θ) of S protein over the nano-particle's surface was extracted and all showed relatively small coverage values ( Θ ~ 0.30). The SPR band peak shift was also examined as the pH values were hopped between pH ~ 3 and pH ~ 10 (pH hopping). As the pH values hopped, an alternation of the average SPR band peaks were observed. A significant amplitude of an alternation was especially observed for the mixture of S protein with gold ≥30 nm of gold size implying the reproduction of pH induced reversible protein folding. We hypothesize that the pH hopping scheme captured a reversible transition between folded or Down conformation (pH ≥ ~7) and unfolded or Up (pH ~ 3) conformation of RBD (receptor binding domain). The acidic condition may also dimerize the S protein through RBD. The Up conformation or dimerization of S protein are considered to be connected to the other gold nano particles forming gold nano-particle aggregates.

Spectroscopic investigation on the affinity of SARS-CoV-2 spike protein to gold nano-particles.

Gold nano-particles were coated with the spike protein (S protein) of SARS-CoV-2 and exposed to increasingly acidic conditions. Their responses were investigated by monitoring the surface plasmon resonance (SPR) band shift. As the external pH was gradually changed from neutral pH to pH ∼2 the peak of the SPR band showed a significant red-shift, with a sigmoidal feature implying the formation of the gold-protein aggregates. The coating of S protein changed the surface property of the gold enough to extract the coverage fraction of protein over nano particles, Θ, which did not exhibit clear nano-size dependence. The geometrical simulation to explain Θ showed the average axial length to be  = 7. 25 nm and  =8.00 nm when the S-protein was hypothesized as a prolate shape with spiking-out orientation. As the pH value externally hopped between pH∼3 and pH∼10, a behavior of reversible protein folding was observed for particles with diameters >30 nm. It was concluded that S protein adsorption conformation was impacted by the size (diameter, d) of a core nano-gold, where head-to-head dimerized S protein was estimated for d ≤ 80 nm and a  in  formation for d = 100 nm.

Nano-size dependence in the adsorption by the SARS-CoV-2 spike protein over gold colloid.

The adsorption process of SARS-CoV-2 Omicron spike protein to the nano-gold colloid surfaces was examined by monitoring the surface plasmon resonance (SPR) band shift of gold-nano particles ranging between diameters of d = 10-100 nm. The externally changed pH between 3 and 11 at 24.5 ± 0.4 °C initiated a reversible formation of the gold colloid aggregates, where formation/deformation of the aggregates were monitored by red/blue shift of the peak of the SPR band. There was no sign of reversible aggregation for d = 10, 15, and 20 nm gold colloids. A clear undulation of the peak shift corresponding to pH hopping between pH ~3 and ~11 was confirmed for colloidal d > 30 nm. This degree of the reversibility was compared to previously reported SARS-CoV-2 Alpha spike protein coated gold colloids. It was concluded that Omicron spike protein possesses a similar low affinity for gold nano particle d < 20 nm and possesses the higher affinity to the gold nanoparticles of d > 30 nm. However, the Omicron spike protein conformation was presumed to be more denatured compared to the SARS-CoV-2 Alpha spike protein. Our finding suggested Omicron spike protein was more acid labile/flexible.

Nano-size dependent protein corona formation by SARS-CoV-2 Omicron spike protein over gold nano-colloid and reversible aggregation.

Amyloid beta (Aβ) peptides, such as Aβ or Aβ are regarded as hallmark neuropathological biomarkers associated with Alzheimer's disease (AD). The formation of an aggregates by Aβ or Aβ-coated gold nano-particles are hypothesized to contain conformation of Aβ oligomers, which could exist only at an initial stage of fibrillogenesis.

An approach for in-situ detection of gold colloid aggregates amyloid formations within the hippocampus of the Cohen's Alzheimer's disease rat model by surface enhanced raman scattering methods.

Amyloid fibrillogenesis is a pathogenic protein aggregation process that occurs through a highly ordered process of protein-protein interactions. To better understand the protein-protein interactions involved in amyloid fibril formation, we formed nanogold colloid aggregates by stepwise additions of ∼2 nmol of amyloid β 1-40 peptide (Aβ) at pH ∼3.7 and ∼25 °C. The processes of protein corona formation and building of gold colloid [diameters () of 20 and 80 nm] aggregates were confirmed by a red-shift of the surface plasmon resonance (SPR) band, λ, as the number of Aβ peptides [(Aβ)] increased. The normalized red-shift of λ, Δλ, was correlated with the degree of protein aggregation, and this process was approximated as the adsorption isotherm explained by the Langmuir-Freundlich model. As the coverage fraction (θ) was analyzed as a function of ϕ, which is the (Aβ) per total surface area of nanogold colloids available for adsorption, the parameters for explaining the Langmuir-Freundlich model were in good agreement for both 20 and 80 nm gold, indicating that ϕ could define the stage of the aggregation process. Surface-enhanced Raman scattering (SERS) imaging was conducted at designated values of ϕ and suggested that a protein-gold surface interaction during the initial adsorption stage may be dependent on the nanosize. The 20 nm gold case seems to prefer a relatively smaller contacting section, such as a -C-N or C═C bond, but a plane of the benzene ring may play a significant role for 80 nm gold. Regardless of the size of the particles, the β-sheet and random coil conformations were considered to be used to form gold colloid aggregates. The methodology developed in this study allows for new insights into protein-protein interactions at distinct stages of aggregation.

Kazushige Yokoyama

Department of Chemistry and Biochemistry

State University of New York Geneseo College

Characterization of pH-Dependent Reversible Self-Assembly of Amyloid Beta 1-40-Coated Gold Colloids

Kazushige Yokoyama

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Chemistry and Biochemistry

State University of New York Geneseo College

Characterization of pH-Dependent Reversible Self-Assembly of Amyloid Beta 1-40-Coated Gold Colloids

Department of Chemistry and Biochemistry