Hyperoxidation of Peroxiredoxins and Effects on Physiology of Drosophila

Abstract

The catalytic activity of peroxiredoxins (Prx) is determined by the conserved peroxidatic cysteine (CysP), which reacts with peroxides to form sulfenic acid (Cys-SOH). Under conditions of oxidative stress, CysP is oxidized to catalytically inactive sulfinic (Cys-SO2) and sulfonic (Cys-SO3) forms. The Cys-SO2 form can be reduced in a reaction catalyzed by sulfiredoxin (Srx). To explore the physiological significance of peroxiredoxin overoxidation, we investigated daily variations in the oxidation state of 2-Cys peroxiredoxins in flies of different ages, or under conditions when the pro-oxidative load is high. We found no statistically significant changes in the 2-Cys Prxs monomer:dimer ratio, which indirectly reflects changes in the Prx catalytic activity. However, we found daily variations in Prx-SO2/3 that were more pronounced in older flies as well as in flies lacking Srx. Unexpectedly, the srx mutant flies did not exhibit a diminished survivorship under normal or oxidative stress conditions. Moreover, the srx mutant was characterized by a higher physiological activity. In conclusion, catalytically inactive forms of Prx-SO2/3 serve not only as a marker of cellular oxidative burden, but may also play a role in an adaptive response, leading to a positive effect on the physiology of Drosophila melanogaster.

Antioxidant enzymes that target hydrogen peroxide are conserved across the animal kingdom, from sponges to mammals

“…3 ). In mammals, mitochondrially-localised PRX3 is predicted to compensate PRX5 functioning (Table 1 ) 53 , and D. melanogaster mutants lacking PRX3 show few effects, supporting a functional redundancy of PRX5 and PRX3 54 .…”

“…Indeed, it is known in mammals that not all AhpC-PRX1 genes are equally sensitive to hyperoxidation; isoforms PRX1, PRX2, and PRX3 are most susceptible 59 , 60 , 61 , whilst PRX4 and PRX5 are more resistant, with PRX4 being protected within the ER 53 , 62 , 63 . In marine demosponges, PRX4 is the only AhpC-PRX1 that we identified, and in two of these species it was predicted to localise extracellularly so would not be protected within the ER (Fig.…”

“…Alternatively, species may encode PRXs that are sensitive to hyperoxidation but that are not reactivated, given that reactivation may not always confer increased fitness. In SRX-depleted D. melanogaster , McGinnis et al 53 demonstrated that PRX hyperoxidation does not adversely affect resistance to oxidative stress or fly lifespan, but instead results in increased physical fitness and endurance. This result was very surprising given the number of studies that have demonstrated reduced fitness from SRX under expression in cell cultures, plants, and mammals 65 , 66 , 67 .…”

“…This result was very surprising given the number of studies that have demonstrated reduced fitness from SRX under expression in cell cultures, plants, and mammals 65 , 66 , 67 . One possible explanation is that hyperoxidized PRXs in the SRX mutant could either signal as damage associated molecular patterns (DAMPs) themselves or alter post-translation modifications of other proteins that in turn signal as DAMPs, to induce beneficial response pathways 53 . DAMPs serve as alarm signals within the innate immune system, alerting cells to any damage or to the presence of non-native microbes, which in turn activates host immune responses 68 .…”

“…One possible explanation is that, despite encoding the GGLG and YF motifs, the susceptibility to hyperoxidation for each of these 10 species may in fact be sufficiently low that AhpC-PRX1 inactivation does not occur. Indeed, it is known in mammals that not all AhpC-PRX1 genes are equally sensitive to hyperoxidation; isoforms PRX1, PRX2, and PRX3 are most susceptible 59,60,61 , whilst PRX4 and PRX5 are more resistant, with PRX4 being protected within the ER 53,62,63 . In marine demosponges, PRX4 is the only AhpC-PRX1 that we identified, and in two of these species it was predicted to localise extracellularly so would not be protected within the ER (Fig.…”