The Role of Methionine Sulfoxide Reductase in the Thermal Stress Response of Drosophila melanogaster
Methionine sulfoxide reductase (Msr) is an enzyme that is used by the majority of organisms to reverse oxidative damage caused by reactive oxygen species (ROS). ROS are free radicals which react with electron-rich molecules such as nucleotides, carbohydrates, or proteins. The highly electronegative amino acid methionine is frequently oxidized to methionine sulfoxide (met-(o)) by ROS; Msr can repair the damaged methionine by reducing met-(o) to functional methionine. There are two distinct enzymes, MsrA and MsrB, which reduce the two enantiomers of met-(o), met-S-(o) and met-R-(o), respectively.
Since additional ROS are produced during an organism’s exposure to thermal stress, we investigated whether MsrA and/or MsrB play a role in the response to thermal stress. Drosophila melanogaster lacking both MsrA and MsrB were found to be less efficient in their thermal stress response when compared to wild-type, suggesting that MsrA and MsrB may play a role in thermal stress response. In addition to MsrA and MsrB, some heat shock proteins (HSPs), especially Hsp70, help mitigate the damaging effects of thermal stress. HSPs are upregulated during periods of hyperthermia and help to maintain protein integrity and provide neuronal protection. Thus, we also examined the possibility that HSP upregulation prior to exposure to hyperthermic conditions improves thermal stress response and survival in Drosophila lacking MsrA and MsrB. Hyperthermic preconditioning was shown to worsen the thermal stress response of D. melanogaster lacking MsrA or MsrB, as well as the wild-type. Future studies include examining the biochemical mechanisms that govern the effect of MsrA and MsrB on hyperthermia tolerance. By determining the roles of MsrA and MsrB in hyperthermia tolerance, we should obtain insight into the multiple functions of MsrA and MsrB throughout an organism.