Raman spectroscopic studies of hen egg-white lysozyme at high temperatures and pressures

Picosecond Bessel Beam Fabricated Pure, Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules

A zeroth-order, non-diffracting Bessel beam, generated by picosecond laser pulses (1064 nm, 10 Hz, 30 ps) through an axicon, was utilized to perform pulse energy-dependent (12 mJ, 16 mJ, 20 mJ, 24 mJ) laser ablation of silver (Ag) substrates in air. The fabrication resulted in finger-like Ag nanostructures (NSs) in the sub-200 nm domain and obtained structures were characterized using the FESEM and AFM techniques. Subsequently, we employed those Ag NSs in surface-enhanced Raman spectroscopy (SERS) studies achieving promising sensing results towards trace-level detection of six different hazardous materials (explosive molecules of picric acid (PA) and ammonium nitrate (AN), a pesticide thiram (TH) and the dye molecules of Methylene Blue (MB), Malachite Green (MG), and Nile Blue (NB)) along with a biomolecule (hen egg white lysozyme (HEWL)). The remarkably superior plasmonic behaviour exhibited by the AgNS corresponding to 16 mJ pulse ablation energy was further explored. To accomplish a real-time application-oriented understanding, time-dependent studies were performed utilizing the AgNS prepared with 16 mJ and TH molecule by collecting the SERS data periodically for up to 120 days. The coated AgNSs were prepared with optimized gold (Au) deposition, accomplishing a much lower trace detection in the case of thiram (~50 pM compared to ~50 nM achieved prior to the coating) as well as superior EF up to ~108 (~106 before Au coating). Additionally, these substrates have demonstrated superior stability compared to those obtained before Au coating.

The Effects of Low-Dose Irradiation on Human Saliva: A Surface-Enhanced Raman Spectroscopy Study

Biological effects of low-dose ionizing radiation (IR) have been unclear until now. Saliva, because of the ease of collection, could be valuable in studying low-dose IR effects by means of surface-enhanced Raman spectroscopy (SERS). The objective of our study was to compare the salivary SER spectra recorded before and after low-dose IR exposure in the case of pediatric patients (PP). Unstimulated saliva was collected from ten PP before and after irradiation with a cone beam computed tomography (CBCT) machine used for diagnostic purposes. The SERS measurements have been recorded on dried saliva samples using a solid nanosilver plasmonic substrate synthesized using an original method developed in our laboratory. The experimental results showed that salivary SER spectra are dominated by three vibrational bands (441,735 and 2107 cm^-1) that can be assigned to bending and stretching vibrations of salivary thiocyanate (SCN-). After exposure, an immediate increase of vibrational bands assigned to SCN- has been recorded in the case of all samples, probably as a result of IR interaction with oral cavity. This finding suggests that SCN- could be used as a valuable biomarker for the detection and identification of low-dose radiation effects.

Pressure effects on collective density fluctuations in water and protein solutions

Neutron Brillouin scattering and molecular dynamics simulations have been used to investigate protein hydration water density fluctuations as a function of pressure. Our results show significant differences between the pressure and density dependence of collective dynamics in bulk water and in concentrated protein solutions. Pressure-induced changes in the tetrahedral order of the water HB network have direct consequences for the high-frequency sound velocity and damping coefficients, which we find to be a sensitive probe for changes in the HB network structure as well as the wetting of biomolecular surfaces.

Appearance of annular ring-like intermediates during amyloid fibril formation from human serum albumin

The self-assembly of proteins triggered by a conformational switch into highly ordered β-sheet rich amyloid fibrils has captivated burgeoning interest in recent years due to the involvement of amyloids in a variety of human diseases and a diverse range of biological functions. Here, we have investigated the mechanism of fibrillogenesis of human serum albumin (HSA), an all-α-helical protein, using an array of biophysical tools that include steady-state as well as time-resolved fluorescence, circular dichroism and Raman spectroscopy in conjunction with atomic force microscopy (AFM). Investigations into the temporal evolution of nanoscale morphology using AFM revealed the presence of ring-like intermediates that subsequently transformed into worm-like fibrils presumably by a ring-opening mechanism. Additionally, a multitude of morphologically-diverse oligomers were observed on the pathway to amyloid formation. Kinetic analysis using multiple structural probes in-tandem indicated that HSA amyloid assembly is a concerted process encompassing a major structural change that is primarily mediated by hydrophobic interactions between thermally-induced disordered segments originating in various domains. A slower growth kinetics of aggregates suggested that the protein structural reorganization is a prerequisite for fibril formation. Moreover, time-dependent Raman spectroscopic studies of HSA aggregation provided key molecular insights into the conformational transitions occurring within the protein amide backbone and at the residue-specific level. Our data revealed the emergence of conformationally-diverse disulfides as a consequence of structural reorganization and sequestration of tyrosines into the hydrophobic amyloid core comprising antiparallel cross β-sheets.

Preparation and characterisation of spray-dried and crystallised trypsin: FT-Raman study to detect protein denaturation after thermal stress

The production of stable protein formulations is difficult due to unique properties of proteins. Accordingly, spray drying and crystallisation techniques were assessed for their effects on trypsin, a model protein. Samples were investigated using polarising microscopy, thermogravimetry, differential scanning calorimetry (DSC), FT-Raman spectroscopy and enzymatic assay. Unprocessed, spray-dried and crystallised trypsin were evaluated in solution for secondary structure in low and high protein concentrations using aqueous state FT-Raman spectroscopy and for folding reversibility employing high sensitivity differential scanning calorimetry. Spray-dried trypsin showed FT-Raman spectral changes and less biological activity, after rehydration, compared with unprocessed and crystallised trypsin. Crystals maintained activity better than did the spray-dried form and retained a higher folding reversibility compared to unprocessed and spray-dried protein. Proteins may denature with structural changes under thermal stress and lose their activities. Thus, this research studied the effect of heating solid unprocessed, spray-dried and crystallised trypsin samples on their secondary structures, using FT-Raman spectroscopy, to identify the influence of the initial solid form on its propensity for thermal denaturation and whether this can be correlated with catalytic activity. DSC heated protein samples to two temperatures, one before the apparent denaturation temperature (T(m)) and the other after the T(m). Samples heated below their T(m) showed some perturbations of the secondary structure and some activity, whilst materials rose to the higher temperature were insoluble with complete loss of activity.

Integrity of crystalline lysozyme exceeds that of a spray-dried form

The development of proteins as therapeutic agents is challenging partly due to their inherent instabilities. Consequently, crystallisation and spray drying techniques were assessed to determine their effects on protein integrity using lysozyme as a model protein. Unprocessed, crystallised and spray-dried lysozyme were characterised by: thermal analysis using hot stage microscopy (HSM), differential scanning calorimetry (DSC), high sensitivity differential scanning calorimetry (HSDSC) and thermogravimetry (TGA); and spectroscopic analysis employing Fourier transform Raman (FT-Raman). Moisture contents were determined by TGA and Karl Fisher titration (KFT). Enzymatic assay measured biological activity. HSM showed no changes in crystals until complete melting. TGA and KFT indicated that spray-dried lysozyme contained a lower moisture content than crystals, hence the higher apparent thermal stability was shown by DSC. HSDSC revealed that crystallisation and spray drying did not affect the denaturation temperature of lysozyme in solution when compared with unprocessed material. However, in the solid state, FT-Raman spectra showed perturbation of the conformational structure of spray-dried sample, whereas crystal conformation remained intact. Enzymatic assay revealed increased activity retention of crystals compared with spray-dried powder. Hence, crystals maintained the conformational integrity and activity of lysozyme in solution.

Protein structure and dynamics at high pressure

The effect of pressure on the structure and dynamics of proteins is discussed in the framework of the pressure-temperature stability phase diagram. The elastic (reversible) properties, thermal expansion, compressibility and heat capacity, are correlated with the entropy, volume, and the coupling between entropy and volume fluctuations respectively. The experimental approaches that can be used to measure these quantities are reviewed. The plastic (conformational) changes reflect the changes in these properties in the cold, pressure and heat denaturation.

Real-time in situ monitoring of lysozyme during lyophilization using infrared spectroscopy: dehydration stress in the presence of sucrose

PURPOSE

First, to investigate the role of sucrose in stabilizing protein structure (as measured by changes in the amide I band of lysozyme) caused by dehydration encountered during lyophilization. Second, to demonstrate the utility of internal reflection spectroscopy as a tool for conducting controlled lyophilization experiments.

METHODS

A custom-built internal reflection FTIR accessory was used to follow the entire freeze-drying process of solutions consisting of 49.4 mg/mL lysozyme in the presence and absence of 10% sucrose in real-time. Studies were carried out using D2O as a transparent medium in the infrared region of the protein amide bands. Potential self-association of the protein in the presence of sucrose was investigated using dynamic light scattering. Hydration levels were determined using a multiple regression equation. Differential scanning calorimetry (DSC) permitted characterization of the final lyophilized product. Moisture content was determined using Karl Fischer titration.

RESULTS

Throughout freezing and drying, minimal changes were observed both in frequency (1647 +/- 1 cm-1) and bandwidth (46 +/- 1 cm-1) of the amide I band in the presence of sucrose. In contrast, greater changes in frequency and band width were seen in the absence of sucrose. A successfully lyophilized cake was obtained which had properties of a glass as measured by DSC, with a Tg of 50 degree C. The lyophilized product containing sucrose had 4% moisture by weight. Three distinct rates of water desorption were discovered during drying under vacuum (50 mg/hr within the sample temperature range from -35 degrees to -25 degrees C; 30 mg/hr from -10 degrees to 25 degrees C; 1.2 mg/hr from 27 degrees to 38 degrees C).

CONCLUSIONS

The inclusion of sucrose served to minimize perturbations of protein structure caused by freezing and dehydration stresses encountered during lyophilization (compared to studies conducted in absence of sucrose). The results support the water replacement hypothesis and underscore the role of the sugar in preserving a native structure in the dried state. This investigation demonstrates the usefulness of infrared spectroscopy in evaluating lyophilization process parameters and formulation design.

Effect of temperature and pressure on yeast invertase stability: a kinetic and conformational study

Kinetics of the temperature- or pressure-induced denaturation of invertase from Saccharomyces cerevisiae were obtained in the temperature range 45-70 degrees C and in the pressure range 500-650 MPa. The investigation was done by measuring the residual activities after cooling or pressure release and the intrinsic fluorescence of aromatic amino-acids (tyrosine and tryptophan) upon excitation at 277 nm. The residual activity decreased exponentially as a function of time incubation according to a biphasic model either with pressure or temperature, whereas the fluorescence emission indicated a difference between these two parameters. When the enzyme was subjected to thermal treatment, the fluorescence of tyrosine and tryptophan decreased slowly, while after high-pressure treatment, these aromatic residues become more exposed to the aqueous solvent during unfolding, giving rise to a large decrease in fluorescence in the 330-340 nm region. Moreover, in the latter case, an enhancement of light scattering intensity showed changes in protein-protein interactions.