Reaction of ozone with protein tryptophans: band III, serum albumin, and cytochrome C

Protein Cross-Linking and Oligomerization through Dityrosine Formation upon Exposure to Ozone

Air pollution is a potential driver for the increasing prevalence of allergic disease, and post-translational modification by air pollutants can enhance the allergenic potential of proteins. Here, the kinetics and mechanism of protein oligomerization upon ozone (O3) exposure were studied in coated-wall flow tube experiments at environmentally relevant O3 concentrations, relative humidities and protein phase states (amorphous solid, semisolid, and liquid). We observed the formation of protein dimers, trimers, and higher oligomers, and attribute the cross-linking to the formation of covalent intermolecular dityrosine species. The oligomerization proceeds fast on the surface of protein films. In the bulk material, reaction rates are limited by diffusion depending on phase state and humidity. From the experimental data, we derive a chemical mechanism and rate equations for a kinetic multilayer model of surface and bulk reaction enabling the prediction of oligomer formation. Increasing levels of tropospheric O3 in the Anthropocene may promote the formation of protein oligomers with enhanced allergenicity and may thus contribute to the increasing prevalence of allergies.

Changes in fluorescence spectra of bioaerosols exposed to ozone in a laboratory reaction chamber to simulate atmospheric aging

A laboratory system for exposing aerosol particles to ozone and rapidly measuring the subsequent changes in their single-particle fluorescence is reported. The system consists of a rotating drum chamber and a single-particle fluorescence spectrometer (SPFS) utilizing excitation at 263 nm. Measurements made with this system show preliminary results on the ultra-violet laser-induced-fluorescence (UV-LIF) spectra of single aerosolized particles of Yersinia rohdei, and of MS2 (bacteriophage) exposed to ozone. When bioparticles are exposed in the chamber the fluorescence emission peak around 330 nm: i) decreases in intensity relative to that of the 400-550 nm band; and ii) shifts slightly toward shorter-wavelengths (consistent with further drying of the particles). In these experiments, changes were observed at exposures below the US Environmental Protection Agency (EPA) limits for ozone.

In vitro exposure of proteins to ozone

An in vitro system has been developed to expose proteins to ozone. The system is designed to deliver consistent and accurate levels of ozone over a range of concentrations (between 0.1 and >/=10 ppm) with extended exposure times (24 h or longer) in a humidified environment (100%). In the experiment presented in this article, ozone concentrations between 0.1 and 2.0 ppm were used. Ozone was generated by an electrical discharge ozonizer to ensure stability; it was continually monitored by an ultraviolet ozone analyzer and was precisely controlled by mass flow controllers, which gave reproducible results between runs. Humidity was closely regulated in the system to allow small amounts of protein solutions (50 muL or less) to be exposed without significant changes (<0.2%) in sample volume. The degree of surfactant protein-A (SP-A) oxidation by ozone was measured between runs to demonstrate the reproducibility of the system. A detailed description of the system is given, and protein oxidation detection methods and their limitations are discussed. Using these methods, we were able to assess oxidation of SP-A that apparently occurred prior to its isolation from the lung by bronchoalveolar lavage. This in vitro system allowed us to expose small amounts of protein to ozone in a simple, highly controlled, and reproducible manner.

Fragmentation mechanisms of oxidized peptides elucidated by SID, RRKM modeling, and molecular dynamics

The gas-phase fragmentation reactions of singly charged angiotensin II (AngII, DR(+)VYIHPF) and the ozonolysis products AngII+O (DR(+)VY*IHPF), AngII+3O (DR(+)VYIH*PF), and AngII+4O (DR(+)VY*IH*PF) were studied using SID FT-ICR mass spectrometry, RRKM modeling, and molecular dynamics. Oxidation of Tyr (AngII+O) leads to a low-energy charge-remote selective fragmentation channel resulting in the b(4)+O fragment ion. Modification of His (AngII+3O and AngII+4O) leads to a series of new selective dissociation channels. For AngII+3O and AngII+4O, the formation of [MH+3O](+)-45 and [MH+3O](+)-71 are driven by charge-remote processes while it is suggested that b(5) and [MH+3O](+)-88 fragments are a result of charge-directed reactions. Energy-resolved SID experiments and RRKM modeling provide threshold energies and activation entropies for the lowest energy fragmentation channel for each of the parent ions. Fragmentation of the ozonolysis products was found to be controlled by entropic effects. Mechanisms are proposed for each of the new dissociation pathways based on the energies and entropies of activation and parent ion conformations sampled using molecular dynamics.

Peptide ozonolysis: product structures and relative reactivities for oxidation of tyrosine and histidine residues

Angiotensin II (DRVYIHPF) and two analogs, (DRVYIAPA and DRVAIHPA), were used as model systems to study the ozonolysis of peptides containing tyrosine and histidine residues. The ESI mass spectrum of angiotensin II following exposure to ozone showed the formation of adducts containing one, three, and four oxygen atoms. CID and SID spectra of these adducts were consistent with formation of Tyr + O and His + 3O as expected from previous work with amino acids. However, several fragment ions observed in the CID and SID spectra suggested formation of a rather unexpected adduct, Tyr + 3O, and a small amount of the Phe + O adduct. These findings were confirmed by examining two angiotensin analogs. Exposure of DRVYIAPA to ozone resulted in the addition of either one or three oxygen atoms on Tyr, while DRVAIHPA showed only the addition of three oxygen atoms--all on His. Other noteworthy minor oxidation products were observed from these analogs including Tyr + 34 Da, His + 5 Da, His + 34 Da, and His + 82 Da. The reaction rates of the peptides with ozone were found to be similar: second-order rate coefficients are 274 +/- 3, 379 +/- 6, and 439 +/- 34 M(-1) s(-1) for DRVYIAPA, DRVAIHPA, and angiotensin II, respectively. The relative rates indicate (1) an isolated His residue has a slightly greater ozone reactivity than an isolated Tyr residue, and (2) the reaction rates of isolated residues are not additive when both residues are present in the same molecule.

Ozone-induced inactivation of antioxidant enzymes

Ozone is an air pollutant that damages a variety of biomolecules. We investigated ozone-induced inactivation of three major antioxidant enzymes. Cu/Zn superoxide dismutase was inactivated by ozone in a concentration-dependent manner. The concentration of ozone for 50% inactivation was approximately 45 microM when 10 microM Cu/Zn superoxide dismutase was incubated for 30 min in the presence of ozone. SDS-polyacrylamide gel electrophoresis (PAGE) showed that the enzyme was randomly fragmented. Both ascorbate and glutathione were very effective in protecting Cu/Zn superoxide dismutase from ozone-induced inactivation. The other two enzymes, catalase and glutathione peroxidase, were much more resistant to ozone than Cu/Zn superoxide dismutase. The ozone concentrations for 50% inactivation of 10 microM catalase and glutathione peroxidase were 500 and 240 microM, respectively. SDS-PAGE demonstrated that ozone caused formation of high molecular weight aggregates in catalase and dimerization in glutathione peroxidase. Glutathione protected catalase and glutathione peroxidase from ozone but the effective concentrations were much higher than that for Cu/Zn superoxide dismutase. Ascorbate was almost ineffective. The result suggests that, among the three antioxidant enzymes, Cu/Zn superoxide dismutase is a major target for ozone-induced inactivation and both glutathione and ascorbate are very effective in protecting the enzyme from ozone.

Electrospray mass and tandem mass spectrometry identification of ozone oxidation products of amino acids and small peptides

Aqueous ozonation of the 22 most common amino acids and some small peptides were studied by electrospray mass (ESI-MS) and tandem mass spectrometry. After 5 min of ozonation only His, Met, Trp, and Tyr form oxidation products clearly detectable by ESI-MS. For His, the main oxidation product is formed by the addition of three oxygen atoms, His + 30; for Met and Tyr by the addition of one oxygen atom, Met + O and Tyr + O, and for Trp by the addition of two oxygen atoms, Trp + 20. Ozone oxidation occurs rapidly, products are already detected after 30 s of ozonation, and the reactivity order is Met > Trp > Tyr > His. The structures of the oxygen addition products were investigated by electrospray product ion mass spectra, and by comparing these spectra to those of protonated intact amino acids, and when available, to those of model compounds. His + 30 was assigned as 2-amino-4-oxo-4-(3-formylureido)butanoic acid (1) formed by oxidation of the His imidazole ring, Met + O as methionine sulfoxide (2), Trp + 20 as N-formylkynurenine (4), and Tyr + O as a mixture of dihydroxyphenylalanines (7 and 8). Ozonation of peptides show that the same number of oxygen atoms are added as expected from the ozonation of the free amino acids. The product ion mass spectra of both the protonated intact peptides, MH+, and the main ozonation products (M + nO)H+ (n = 1-3) revealed b and y type ions as the main fragments, which allow one to assign the type and location of modified amino acid in the model peptides.

Composition and stability of allergenic extracts made from gamma-irradiated rye grass (Lolium perenne) pollen

BACKGROUND

Phenol is commonly added to allergenic extracts as a bacteriostatic agent, but it is poisonous and also detrimental to proteins, which accelerates extract degradation. Sterilization by gamma-irradiation of the source material could be an alternative to the use of phenol.

OBJECTIVE

To analyse the potential effects of gamma-irradiation of pollen on the composition, potency, and stability of the resulting extract, and compare them with those of phenol.

METHODS

Ryegrass (Lolium perenne) pollen was sterilized by gamma-irradiation at a dose of 25 kGy. Extracts prepared from the irradiated pollen were then compared by electrophoresis techniques and RAST inhibition to extracts, without or with 0.5% phenol, from nonirradiated pollen. In addition, proteolytic activity was compared in extracts from irradiated and nonirradiated pollen. To evaluate the stability of extracts on storage, they were analysed after forced degradation for up to 7 days at 37 degrees C.

RESULTS

When fresh extracts were analysed, there were no noticeable differences between the three types, as judged by immunoblotting and RAST inhibition experiments. However, on storage, extracts from irradiated pollen appeared to be superior to extracts from nonirradiated pollen, as some proteins were more stable in the former. This could be related to the lower proteolytic activity we have also observed in extracts from irradiated pollen. In contrast, extracts containing phenol degraded much faster, as proven by all our methods of investigation.

CONCLUSION

Gamma-irradiation of pollen did not influence the IgE-binding capacity of the resulting extracts, but did yield extracts with somewhat improved stability, probably by reducing the proteolytic activity. It may be concluded that gamma-irradiation of the source material represents a good alternative to the use of phenol for the preparation of allergenic extracts.