Lysozyme fragmentation induced by gamma-radiolysis

Impacts of solvation on photo-damage of polypeptides: Modulation and biological implications

We investigate the photon/matter interactions between soft X-rays and three selected polypeptides, poly-glycine (poly-Gly), poly-L-arginine (poly-Arg), and poly-l-lysine (poly-Lys), where the effects of molecular packing under the influence of solvent, e.g., water, substrates (Au foil or Si wafer) and X-ray irradiation under different durations were systematically investigated. Compared with negligible photo-damage on bare polypeptide powders, significantly enhanced degradation in pre-solvated polypeptides was observed likely because of the formation photo-generated radicals. X-ray photoemission spectroscopy (XPS) were employed as the analysis means to identify and quantify the chemical changes, especially the high-resolution photoemission spectra of C 1s, O 1s, N 1s and their evolution under continuous X-ray irradiation. The photo-degradation was found to preferentially occur on the CO entity in poly-Gly and the guanidinium group in poly-Arg. In poly-Arg, deprotonation occurs via the switch from zwittterionic to a neutral configuration, whereas poly-Lys deprotonates by directly losing the corresponding amine. The critical role of the interactions between amino acids, the building blocks of protein and almost all forms of biological activities, and the free-radical-generating living environment under irradiation was critically analyzed. The present study found that the preparation history of a sample, especially its inadvertent exposure to the sources of H₂O, O₂ and OH, could significantly alter the outcome of a radiation-related chemical process. Implications on the non-destructive probe of biologically important systems using physical methods involving X-rays were discussed as well.

Effects of Gamma and Electron Radiation on the Structural Integrity of Organic Molecules and Macromolecular Biomarkers Measured by Microarray Immunoassays and Their Astrobiological Implications

High-energy ionizing radiation in the form of solar energetic particles and galactic cosmic rays is pervasive on the surface of planetary bodies with thin atmospheres or in space facilities for humans, and it may seriously affect the chemistry and the structure of organic and biological material. We used fluorescent microarray immunoassays to assess how different doses of electron and gamma radiations affect the stability of target compounds such as biological polymers and small molecules (haptens) conjugated to large proteins. The radiation effect was monitored by measuring the loss in the immunoidentification of the target due to an impaired ability of the antibodies for binding their corresponding irradiated and damaged epitopes (the part of the target molecule to which antibodies bind). Exposure to electron radiation alone was more damaging at low doses (1 kGy) than exposure to gamma radiation alone, but this effect was reversed at the highest radiation dose (500 kGy). Differences in the dose-effect immunoidentification patterns suggested that the amount (dose) and not the type of radiation was the main factor for the cumulative damage on the majority of the assayed molecules. Molecules irradiated with both types of radiation showed a response similar to that of the individual treatments at increasing radiation doses, although the pattern obtained with electrons only was the most similar. The calculated radiolysis constant did not show a unique pattern; it rather suggested a different behavior perhaps associated with the unique structure of each molecule. Although not strictly comparable with extraterrestrial conditions because the irradiations were performed under air and at room temperature, our results may contribute to understanding the effects of ionizing radiation on complex molecules and the search for biomarkers through bioaffinity-based systems in planetary exploration.

Physical, Chemical and Biochemical Modifications of Protein-Based Films and Coatings: An Extensive Review

Protein-based films and coatings are an interesting alternative to traditional petroleum-based materials. However, their mechanical and barrier properties need to be enhanced in order to match those of the latter. Physical, chemical, and biochemical methods can be used for this purpose. The aim of this article is to provide an overview of the effects of various treatments on whey, soy, and wheat gluten protein-based films and coatings. These three protein sources have been chosen since they are among the most abundantly used and are well described in the literature. Similar behavior might be expected for other protein sources. Most of the modifications are still not fully understood at a fundamental level, but all the methods discussed change the properties of the proteins and resulting products. Mastering these modifications is an important step towards the industrial implementation of protein-based films.

Enhancement of Chaperone Activity of Plant-Specific Thioredoxin through γ-Ray Mediated Conformational Change

AtTDX, a thioredoxin-like plant-specific protein present in Arabidospis is a thermo-stable and multi-functional enzyme. This enzyme is known to act as a thioredoxin and as a molecular chaperone depending upon its oligomeric status. The present study examines the effects of γ-irradiation on the structural and functional changes of AtTDX. Holdase chaperone activity of AtTDX was increased and reached a maximum at 10 kGy of γ-irradiation and declined subsequently in a dose-dependent manner, together with no effect on foldase chaperone activity. However, thioredoxin activity decreased gradually with increasing irradiation. Electrophoresis and size exclusion chromatography analysis showed that AtTDX had a tendency to form high molecular weight (HMW) complexes after γ-irradiation and γ-ray-induced HMW complexes were tightly associated with a holdase chaperone activity. The hydrophobicity of AtTDX increased with an increase in irradiation dose till 20 kGy and thereafter decreased further. Analysis of the secondary structures of AtTDX using far UV-circular dichroism spectra revealed that the irradiation remarkably increased the exposure of β-sheets and random coils with a dramatic decrease in α-helices and turn elements in a dose-dependent manner. The data of the present study suggest that γ-irradiation may be a useful tool for increasing holdase chaperone activity without adversely affecting foldase chaperone activity of thioredoxin-like proteins.

Temperature-dependent radiation sensitivity and order of 70S ribosome crystals

All evidence to date indicates that at T = 100 K all protein crystals exhibit comparable sensitivity to X-ray damage when quantified using global metrics such as change in scaling B factor or integrated intensity versus dose. This is consistent with observations in cryo-electron microscopy, and results because nearly all diffusive motions of protein and solvent, including motions induced by radiation damage, are frozen out. But how do the sensitivities of different proteins compare at room temperature, where radiation-induced radicals are free to diffuse and protein and lattice structures are free to relax in response to local damage? It might be expected that a large complex with extensive conformational degrees of freedom would be more radiation sensitive than a small, compact globular protein. As a test case, the radiation sensitivity of 70S ribosome crystals has been examined. At T = 100 and 300 K, the half doses are 64 MGy (at 3 Å resolution) and 150 kGy (at 5 Å resolution), respectively. The maximum tolerable dose in a crystallography experiment depends upon the initial or desired resolution. When differences in initial data-set resolution are accounted for, the former half dose is roughly consistent with that for model proteins, and the 100/300 K half-dose ratio is roughly a factor of ten larger. 70S ribosome crystals exhibit substantially increased resolution at 100 K relative to 300 K owing to cooling-induced ordering and not to reduced radiation sensitivity and slower radiation damage.

Physico-chemical characteristics of gamma-irradiated gelatin

This article reports the effects of gamma irradiation (dose ranges 0.1–10 kGy from ⁶⁰Co source) on the characteristics of solid gelatin and the physico-mechanical, microstructural and bioactive properties of the scaffold prepared from irradiated gelatin solution. FTIR, intrinsic viscosity, bloom strength, thermal properties, SEM, tensile properties, water uptake ability and antimicrobial activities of non-irradiated and irradiated solid gelatin and its scaffolds were investigated. The detailed experimental results for the solid gelatin demonstrated that 1 kGy γ-irradiated samples showed higher intrinsic viscosity, enhanced thermal stability and bloom strength than other irradiated samples. Furthermore, the scaffold thus prepared from irradiated and non-irradiated gelatin also revealed that 1 kGy samples showed the highest tensile strength and modulus with good water resistivity than other irradiated and non-irradiated samples. In addition to the physico-mechanical properties, 1 kGy scaffolds have also exhibited the highest resistivity towards microbial growth that can have potentiality as scaffold in biomedical sector. The enhanced functional and bioactive properties at low irradiation doses (1 kGy) may occurred due to an initial breaking of hydrogen bonds of polypeptide chains in gelatin molecules that indicated by the shift of amide A, I and II peaks to higher wave numbers in FTIR. This enhancement resulted probably due to the domination of crosslinking over degradation at 1 kGy. It was also observed that 1 kGy γ-radiation-induced crosslinking has lowered the hydrophilicity by decreasing water uptake and mean pore diameter of the interconnected porous structures of gelatin.

Comparison Study on Changes of Antigenicities of Egg Ovalbumin Irradiated by Electron Beam or X-Ray

This study was conducted to compare the effects of two forms of radiation (electron and X-ray; generated by an electron beam accelerator) on the conformation and antigenic properties of hen’s egg albumin, ovalbumin (OVA), which was used as a model protein. OVA solutions (2.0 mg/mL) were individually irradiated by electron beam or X-ray at the absorbed doses of 0 (control), 2, 4, 6, 8, and 10 kGy. No differences between the two forms of radiation on the structural properties of OVA were shown by spectrometric and electrophoretic analyses. The turbidity of OVA solution increased and the main OVA bands on polyacrylamide gels disappeared after irradiation, regardless of the radiation source. In competitive indirect enzyme-linked immunosorbent assay, OVA samples irradiated by electron beam or X-ray showed different immunological responses in reactions with monoclonal and polyclonal antibodies (immunoglobulin G) produced against non-irradiated OVA. The results indicate that electron beam irradiation and X-ray irradiation produced different patterns of structural changes to the OVA molecule.

Optimized enzymatic dual functions of PaPrx protein by proton irradiation

We investigated the effects of proton irradiation on the function and structure of the Pseudomonas aeruginosa peroxiredoxin (PaPrx). Polyacrylamide gel demonstrated that PaPrx proteins exposed to proton irradiation at several doses exhibited simultaneous formation of high molecular weight (HMW) complexes and fragmentation. Size-exclusion chromatography (SEC) analysis revealed that the number of fragments and very low molecular weight (LMW) structures increased as the proton irradiation dose increased. The peroxidase activity of irradiated PaPrx was preserved, and its chaperone activity was significantly increased by increasing the proton irradiation dose. The chaperone activity increased about 3-4 fold after 2.5 kGy proton irradiation, compared with that of non-irradiated PaPrx, and increased to almost the maximum activity after 10 kGy proton irradiation. We previously obtained functional switching in PaPrx proteins, by using gamma rays and electron beams as radiation sources, and found that the proteins exhibited increased chaperone activity but decreased peroxidase activity. Interestingly, in this study we newly found that proton irradiation could enhance both peroxidase and chaperone activities. Therefore, we can suggest proton irradiation as a novel protocol for conserved 2-Cys protein engineering.

Generation of polypeptide-templated gold nanoparticles using ionizing radiation

Ionizing radiation, including γ rays and X-rays, are high-energy electromagnetic radiation with diverse applications in nuclear energy, astrophysics, and medicine. In this work, we describe the use of ionizing radiation and cysteine-containing elastin-like polypeptides (C(n)ELPs, where n = 2 or 12 cysteines in the polypeptide sequence) for the generation of gold nanoparticles. In the presence of C(n)ELPs, ionizing radiation doses higher than 175 Gy resulted in the formation of maroon-colored gold nanoparticle dispersions, with maximal absorbance at 520 nm, from colorless metal salts. Visible color changes were not observed in any of the control systems, indicating that ionizing radiation, gold salt solution, and C(n)ELPs were all required for nanoparticle formation. The hydrodynamic diameters of nanoparticles, determined using dynamic light scattering, were in the range of 80-150 nm, while TEM imaging indicated the formation of gold cores 10-20 nm in diameter. Interestingly, C2ELPs formed 1-2 nm diameter gold nanoparticles in the absence of radiation. Our results describe a facile method of nanoparticle formation in which nanoparticle size can be tailored based on radiation dose and C(n)ELP type. Further improvements in these polypeptide-based systems can lead to colorimetric detection of ionizing radiation in a variety of applications.

Protective role of ascorbic acid in the decontamination of cow milk casein by gamma-irradiation

PURPOSE

The aim of this work was to investigate the protective role of ascorbic acid on irradiation-induced modification of casein.

MATERIALS AND METHODS

Casein stock solutions were irradiated with increasing doses 2-10 kGy using (60)Co Gamma rays at a dose rate D• = 136.73 Gy/min at room temperature. The total viable microorganism content of cow milk casein was evaluated by Plate Count Agar (PCA) incubation for 48 h at 37°C. Sodium dodecylsulfate gel electrophoresis (SDS-PAGE) and Matrix-Assisted Laser Desorption-Ionization Time-of-Flight mass spectrometry (MALDI-TOF-MS) analysis were used to evaluate the effect of gamma irradiation on casein integrity.

RESULTS

Gamma irradiation reduced the bacterial contamination of casein solutions at a lower irradiation dose when performed in the presence of ascorbic acid. The irradiation treatment of casein in the absence of ascorbic acid with a dose of 4 kGy could reduce 99% of the original amount of bacterial colonies. However, in the presence of ascorbic acid the irradiation treatment of casein with a dose lower than 2 kGy could reduce 99% of the original amount of bacterial colonies which suggested that the irradiation dose lower than 2 kGy achieved almost the entire decontamination result. SDS-PAGE and MALDI-TOF-MS analysis showed that ascorbic acid protected cow milk casein from degradation and subsequent aggregation probably by scavenging oxygen and protein radicals produced by the irradiation.

CONCLUSIONS

It is demonstrated that the combination of gamma irradiation and ascorbic acid produce additive effects, providing acceptable hygienic quality of cow milk casein and protects caseins against Reactive Oxygen Species (ROS) generated, during the irradiation process.

Spatial distribution of radiation damage to crystalline proteins at 25-300 K

The spatial distribution of radiation damage (assayed by increases in atomic B factors) to thaumatin and urease crystals at temperatures ranging from 25 to 300 K is reported. The nature of the damage changes dramatically at approximately 180 K. Above this temperature the role of solvent diffusion is apparent in thaumatin crystals, as solvent-exposed turns and loops are especially sensitive. In urease, a flap covering the active site is the most sensitive part of the molecule and nearby loops show enhanced sensitivity. Below 180 K sensitivity is correlated with poor local packing, especially in thaumatin. At all temperatures, the component of the damage that is spatially uniform within the unit cell accounts for more than half of the total increase in the atomic B factors and correlates with changes in mosaicity. This component may arise from lattice-level, rather than local, disorder. The effects of primary structure on radiation sensitivity are small compared with those of tertiary structure, local packing, solvent accessibility and crystal contacts.

Can radiation damage to protein crystals be reduced using small-molecule compounds?

Recent studies have defined a data-collection protocol and a metric that provide a robust measure of global radiation damage to protein crystals. Using this protocol and metric, 19 small-molecule compounds (introduced either by cocrystallization or soaking) were evaluated for their ability to protect lysozyme crystals from radiation damage. The compounds were selected based upon their ability to interact with radiolytic products (e.g. hydrated electrons, hydrogen, hydroxyl and perhydroxyl radicals) and/or their efficacy in protecting biological molecules from radiation damage in dilute aqueous solutions. At room temperature, 12 compounds had no effect and six had a sensitizing effect on global damage. Only one compound, sodium nitrate, appeared to extend crystal lifetimes, but not in all proteins and only by a factor of two or less. No compound provided protection at T=100 K. Scavengers are ineffective in protecting protein crystals from global damage because a large fraction of primary X-ray-induced excitations are generated in and/or directly attack the protein and because the ratio of scavenger molecules to protein molecules is too small to provide appreciable competitive protection. The same reactivity that makes some scavengers effective radioprotectors in protein solutions may explain their sensitizing effect in the protein-dense environment of a crystal. A more productive focus for future efforts may be to identify and eliminate sensitizing compounds from crystallization solutions.

Identification of outer membrane proteins of Vibrio parahaemolyticus and Vibrio alginolyticus altered in response to γ-irradiation or long-term starvation

Vibrio parahaemolyticus and Vibrio alginolyticus were subjected to γ-irradiation (0.5 kGy) or starvation by incubation for 8 months in seawater to study modifications in their outer membrane protein patterns. After treatment, outer membrane protein profiles of starved or γ-irradiated bacteria were found to be altered when analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Altered proteins were identified by mass spectrometry (MS and MS/MS) and analyses revealed that OmpU can be considered a starvation stress-induced protein. In addition, expression of OtnA, OmpW, OmpA and peptidoglycan-associated lipoprotein decreased to non-detectable levels in starved cells. Furthermore, MltA-interacting protein MipA appeared under γ-irradiation or starvation conditions. Thus, it can be considered to be a γ-irradiation, long-term starvation stress protein in some vibrios.

Alterations of outer membrane proteins and virulence genes expression in gamma-irradiated Vibrio parahaemolyticus and Vibrio alginolyticus

Gamma-irradiation technology sterilizes microorganisms and thereby prevents decay and improves the safety and shelf stability of food products. In this study we treated the foodborne pathogens Vibrio parahaemolyticus and Vibrio alginolyticus with gamma-irradiation (0.5 kGy) to evaluate their adaptative response. Outer membrane protein patterns of irradiated bacteria were found altered when analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. These modifications were manifested by the appearance and/or disappearance of bands as well as in the expression level of certain proteins. In addition, we searched for the presence of eight Vibrio cholerae virulence genes, toxR, toxS, toxRS, ctxA, zot, ace, toxT, and virulence pathogenicity island (VPI), in the genome of investigated strains. The expression of toxR, toxS, VPI, and ace genes in gamma-irradiated bacteria, studied by reverse transcriptase polymerase chain reaction, was altered. These variations were manifested by an increase and/or a decrease in the expression level of tested virulence genes.

Biodegradable zein-based films: influence of gamma-irradiation on structural and functional properties

Zein, a predominant corn protein, is an alcohol-soluble protein extracted from corn and is characterized by unique film-forming properties. The characteristic brittleness of zein diminishes its usefulness as a structural material. The objective of this work was to study the effect of gamma-irradiation on improving the performance of zein films in packaging applications. This goal has been achieved by irradiating zein film-forming solutions with various doses of gamma-rays, namely, 10, 20, 30, and 40 kGy at dose rate of 10.5 kGy/h, using a Co(60) gamma-radiation source. The impact of radiation process on the structural properties has been explored through far-UV CD spectral analysis and scanning electron microscopy. Additionally, viscosity changes that reflect the effect of radiation treatment on degradation and/or cross-linking of protein chains have been measured. However, improvements in the performance of zein films as packaging materials that can be accomplished by radiation treatment have been investigated via monitoring of the color, surface density, roughness, mechanical properties (tensile strength and elongation percentage), water uptake, and water barrier properties. The results indicated that gamma-irradiation treatment of the film-forming solution can be used to improve the water barrier properties, as well as color and appearance of the zein films. Moreover, a sterilization effect is considered to be an additional advantage for applying gamma- irradiation.

Impact of gamma-radiation on antigenic properties of cow's milk beta-lactoglobulin

This study evaluated the effects of gamma-radiation on the antigenic properties of beta-lactoglobulin in cow's milk. Liquid and lyophilized samples of cow's milk and whey were irradiated with gamma-cells (60Co) at dose levels of 3, 5, and 10 kGy, at room temperature in the presence of air. Effects of treatment on proteins were monitored by Lowry's method, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and enzyme-linked immunosorbent assay. Radiation did not affect the molecular-weight distributions of proteins, but it did reduce their solubility. Furthermore, results showed that irradiation at 10 kGy increased the recognition of milk and whey powders by anti-beta-lactoglobulin (beta-Lg) rabbit immunoglobulin G, with the other samples remaining antigenically stable. These results indicate that gamma-rays do not reduce cow's milk beta-lactoglobulin antigenicity.

The role of ascorbate and histidine in fibrinogen protection against changes following exposure to a sterilizing dose of γ-irradiation

Sodium ascorbate and histidine were employed to protect fibrinogen against modifications followed by a gamma-irradiation process that could potentially inactivate the blood-borne viruses in plasma-derived products. Fibrinogen was irradiated (50 kGy total dose, on dry ice) using a 60Co source. Samples were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blot. Carbonyl groups were measured by the 2,4-dinitrophenylhydrazine-coupled method, and the fibrinogen clotting activity was assessed by different functional assays. In irradiated fibrinogen, the carbonyl group concentration was elevated three-fold versus control; and moderate fragmentation of largely Aalpha and Bbeta chains was revealed. The rate of thrombin-catalyzed fibrinogen polymerization was inhibited (average 50%) with normal fibrinopeptide release and with a minor decrease of total clottable fibrinogen and alpha-polymer formation. Ascorbate reduced the incorporation of carbonyls to the fibrinogen molecule (by > 50% at 50 mmol/l; P < 0.001). Contrary to ascorbate, which alone delayed the fibrinogen polymerization rate, histidine abolished irradiation-induced inhibition of fibrinogen polymerization (by 80% at 50 mmol/l; P < 0.001). In conclusion, even though ascorbate effectively protects fibrinogen from oxidation due to its adverse effects on fibrinogen function, it may not serve as a suitable radioprotective. On the contrary, the first definite evidence is provided that radiation-sterilized fibrinogen in the presence of histidine greatly retains its clotting capability.

Haemostatic properties of human plasma subjected to a sterilizing dose of gamma irradiation in the presence of ascorbate

The objective was to study the effects of gamma irradiation, in the presence of sodium ascorbate, on coagulation/fibrinolytic activity of fresh frozen plasma to be applied to inactivate the transfusion-transmitted viruses in plasma-derived products. Plasma was irradiated (50 kGy total dose, on dry ice) using a 60Co source. The plasma proteins were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blot and the following parameters estimated: prothrombin time, functional fibrinogen concentration, thrombin-induced fibrinogen polymerization, plasminogen activity, and tissue-type plasminogen activator-induced conversion of plasminogen to plasmin. In irradiated plasma a moderate fragmentation of the most labile plasma proteins was found. The prothrombin time was prolonged (1.5-fold), functional fibrinogen was significantly reduced (60%), fibrinogen polymerization was impaired, plasminogen was predominantly maintained (90%) and tissue-type plasminogen activator-induced conversion of plasminogen to plasmin was unchanged. Ascorbate (25 mmol/l) raised the level of functional fibrinogen in irradiated plasma (to 50%; P=0.0245) and slightly accelerated its polymerization. The small protective effect of ascorbate might be due to inhibition of the radiation-induced fibrinogen oxidation and/or fragmentation but addition of other antioxidants/stabilizers would be crucial when a high irradiation dose, an effective treatment for inactivation of the most resistant viruses, is applied.

Study of the interaction of artemisinin with bovine serum albumin

The study on the interaction of artemisinin with bovine serum albumin (BSA) has been undertaken at three temperatures, 289, 296 and 303 K and investigated the effect of common ions and UV C (253.7 nm) irradiation on the binding of artemisinin with BSA. The binding mode, the binding constant and the protein structure changes in the presence of artemisinin in aqueous solution at pH 7.40 have been evaluated using fluorescence, UV-vis and Fourier transform infrared (FT-IR) spectroscopy. The quenching constant K(q), K(sv) and the association constant K were calculated according to Stern-Volmer equation based on the quenching of the fluorescence of BSA. The thermodynamic parameters, the enthalpy (DeltaH) and the entropy change (DeltaS) were estimated to be -3.625 kJ mol(-1) and 107.419 J mol(-1)K(-1) using the van't Hoff equation. The displacement experiment shows that artemisinin can bind to the subdomain IIA. The distance between the tryptophan residues in BSA and artemisinin bound to site I was estimated to be 2.22 nm using Föster's equation on the basis of fluorescence energy transfer. The decreased binding constant in the presence of enough common ions and UV C exposure, indicates that common ions and UV C irradiation have effect on artemisinin binding to BSA.

EPR spectroscopy and theoretical study of gamma-irradiated asparagine and aspartic acid in solid state

Aspartic acid (Asp) and asparagine (Asn) are vulnerable amino acids. One-electron addition or withdrawal reactions initiate many deleterious processes involving these amino acids. To study these redox processes we have irradiated by gamma-rays asparagine or aspartic acid in the solid state. The nature of the resulting free radicals was determined by electron paramagnetic resonance (EPR) and by calculations using DFT methods in various environments. Reactions initiated by electron transfer are different for both amino acids: Asn anion loses hydrogen atom whereas the cation undergoes decarboxylation. Conversely, Asp cation loses hydrogen atom from amine group, which triggers decarboxylation.

Effect of gamma-irradiation on the molecular properties of bovine serum albumin

To investigate the effect of oxygen radicals on the molecular properties of bovine serum albumin (BSA), the secondary and tertiary structures, molecular weight and optical anisotropy of BSA were examined after the irradiation of the protein at various doses. gamma-Irradiation of the protein solution caused the disruption of the ordered structure of protein molecules as well as degradation, cross-linking and aggregation of polypeptide chains. Fluorescence spectroscopy indicated that irradiation quenched the emission intensity excited at 280 nm. Fourier transform infrared spectroscopy (FTIR) indicated that irradiation caused transformation from beta-turns into beta-sheets. A light scattering study showed that increasing the radiation dose decreased the molecular weight of the protein. Optical anisotropy data showed that radiation changed the ordered structure of the protein. Ultraviolet absorption spectroscopy indicated that fragmentation and aggregation might occur in response to radiation exposure.

Electron beam irradiation as protection against the environmental release of recombinant molecules for biomaterials applications

In biomaterials applications there exists a need to protect against the environmental release of recombinant microorganisms and transmissible genetic material and to prevent the recovery of proprietary genetic information. Irradiation technologies have long been used to eliminate microorganisms associated with spoilage and contamination and recent studies have demonstrated that moderate doses of irradiation may be used to sterilize medically important proteins without causing adverse effects in their desirable biological properties. Recombinant Escherichia coli cells expressing organophosphate hydrolase (OPH, E.C. 3.1.8.1), an important enzyme for the detection and decontamination of neurotoxic pesticides and chemical warfare agents, were subjected to electron beam irradiation to gauge its effect on enzymatic activity, cell viability and DNA recoverability. Bacterial samples were irradiated at 2, 20 and 200 kGy using a 10 MeV electron source. Irradiation levels of 2 to 20 kGy were sufficient to eliminate viable cells without affecting OPH enzymatic activity. Biologically active DNA was recovered via PCR from all samples through the 20 kGy irradiation level. While DNA was not recovered from samples at the 200 kGy exposure level, protein activity was reduced by 19 to 78%, depending on the method of cell preparation. These results demonstrate that irradiation can be effective in preventing the release of recombinant organisms intended for use in biomaterials applications without eliminating enzymatic activity and suggests that further research may indicate specific conditions whereby DNA recovery can be eliminated while retaining sufficient enzymatic activity for targeted biomaterials applications.

Effect of gamma-irradiation on the molecular properties of myoglobin

To elucidate the effect of gamma-irradiation on the molecular properties of myoglobin, the secondary and tertiary structures, as well as the molecular weight size of the protein, were examined after irradiation at various irradiation doses. Gamma-irradiation of myoglobin solutions caused the disruption of the ordered structure of the protein molecules, as well as degradation, crosslinking, and aggregation of the polypeptide chains. A SDSPAGE study indicated that irradiation caused initial fragmentation of the proteins and subsequent aggregation, due to cross-linking of the protein molecules. The effect of irradiation on the protein was more significant at lower protein concentrations. Ascorbic acid protected against the degradation and aggregation of proteins by scavenging oxygen radicals that are produced by irradiation. A circular dichroism study showed that an increase of the irradiation decreased the alpha-helical content of myoglobin with a concurrent increase of the aperiodic structure content. Fluorescence spectroscopy indicated that irradiation increased the emission intensity that was excited at 280 nm.

Changes in the antigenic and immunoglobulin E-binding properties of hen's egg albumin with the combination of heat and gamma irradiation treatment

This study was carried out to evaluate the changes in the allergenic and antigenic properties of hen's egg albumin (ovalbumin [OVA]) with the combination of heat and gamma irradiation treatment. OVA solution samples were treated by (i) heating (sample 1), (ii) irradiation after heating (sample 2), and (iii) heating after irradiation (sample 3). Samples were isothermally heated and irradiated at the absorption dose of 10 kGy. Competitive indirect enzyme-linked immunosorbent assays (ELISAs) were performed with blood serum to test the ability of treated OVA to bind to immunoglobulin E (IgE) and mouse murine monoclonal antibody (IgG). OVA's ability to bind to mouse IgG changed upon heating at 75 degrees C, and its ability to bind to egg-allergic IgE changed upon heating at 80 degrees C. The ELISAs showed that egg-allergic IgE did not recognize OVA very well when heated at > or = 80 degrees C, while mouse IgG retained better activity under these conditions. Egg-allergic IgE binding was low both for OVA samples treated by heating and for samples treated by irradiation followed by heating. These results show that allergies induced by OVA could be effectively reduced by the combination of heat and gamma irradiation treatment.

Specific protein dynamics near the solvent glass transition assayed by radiation-induced structural changes

The nature of the dynamical coupling between a protein and its surrounding solvent is an important, yet open issue. Here we used temperature-dependent protein crystallography to study structural alterations that arise in the enzyme acetylcholinesterase upon X-ray irradiation at two temperatures: below and above the glass transition of the crystal solvent. A buried disulfide bond, a buried cysteine, and solvent exposed methionine residues show drastically increased radiation damage at 155 K, in comparison to 100 K. Additionally, the irradiation-induced unit cell volume increase is linear at 100 K, but not at 155 K, which is attributed to the increased solvent mobility at 155 K. Most importantly, we observed conformational changes in the catalytic triad at the active site at 155 K but not at 100 K. These changes lead to an inactive catalytic triad conformation and represent, therefore, the observation of radiation-inactivation of an enzyme at the atomic level. Our results show that at 155 K, the protein has acquired--at least locally--sufficient conformational flexibility to adapt to irradiation-induced alterations in the conformational energy landscape. The increased protein flexibility may be a direct consequence of the solvent glass transition, which expresses as dynamical changes in the enzyme's environment. Our results reveal the importance of protein and solvent dynamics in specific radiation damage to biological macromolecules, which in turn can serve as a tool to study protein flexibility and its relation to changes in a protein's environment.

Effects of gamma radiation on the allergenic and antigenic properties of milk proteins

This study was carried out to evaluate the application of food irradiation technology as a method for reducing milk allergies. Bovine alpha-casein (ACA) and beta-lactoglobulin (BLG) were used as milk proteins. Using milk-hypersensitive patients' immunoglobulin E (IgE) and rabbit IgGs individually produced to ACA and BLG, the changes of allergenicity and antigenicity of irradiated proteins were observed by competitive indirect enzyme-linked immunosorbent assay. Allergenicity and antigenicity of the irradiated proteins were changed with different slopes of the inhibition curves. The disappearance of the band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and increase of the turbidity showed that solubility of the proteins decreased by radiation, and this decrease might be caused by agglomeration of the proteins. These results indicated that epitopes on milk allergens were structurally altered by gamma irradiation.

Effects of gamma radiation on the conformational and antigenic properties of a heat-stable major allergen in brown shrimp

This study was performed to evaluate the application of food irradiation technology as a method for reducing shrimp allergy without adverse effects. Shrimp heat-stable protein (HSP) was isolated and gamma irradiated at 0, 1, 3, 5, 7, or 10 kGy in the condition of solution (1 mg/ml), and fresh shrimp was also irradiated. Conformational change of irradiated HSP was monitored by means of spectrometric measures, enzyme-linked immunosorbent assay with mouse monoclonal antibody, or human patients' sera and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The ability of the immunoglobulin E of patients allergic to shrimp to bind to irradiated HSP was dose dependently reduced. The amount of intact HSP in an irradiated solution was reduced by gamma irradiation, depending on the dose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the main band disappeared and the traces induced from coagulation appeared at a higher molecular weight zone. The binding ability of immunoglobulin E to allergens in the extracts from irradiated shrimp decreased, depending on the dose. The results provide a new method so that food irradiation technology can be applied to reduce allergenicity of shrimp.