Irradiation of GAPDH: a model for environmentally induced protein damage

Abstract

Environmental factors, including sunlight, are able to induce severe oxidative protein damage. The modified proteins are either repaired, degraded or escape from degradation and aggregate. In the present study we tested the effect of different sunlight components such as UV-A, UV-B, and infrared radiation on protein oxidation in vitro. We chose glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a model enzyme and analyzed the irradiation-induced enzyme activity loss, fragmentation and aggregation, and quantified various oxidative amino acid modifications. Since γ-irradiation was used in numerous studies before, we used it for comparative purposes. Infrared radiation was unable to damage GAPDH in the dose range tested (0–1000 J/cm²). UV-A led to a decrease in free thiol content, which was connected with a loss in enzyme activity, while only at very high doses could moderate protein aggregation and fragmentation be observed. UV-B (0–2 J/cm²) and γ-irradiation (0–500 Gy) led to a dose-dependent increase in protein modification. Interestingly, UV-B acted on specific amino acids, such as arginine, proline, and tyrosine, whereas γ-irradiation acted more randomly. The possibility of using the amino acid oxidation pattern as a biomarker of the source of damage is discussed.