Loss of methionine sulfoxide reductase B leads to higher failure rates in Drosophila melanogaster after hyperthermic stress

Syed Raza, James Martin, Lindsay Bruce, David Binninger

Abstract


When an organism is facing excessive metabolic production of heat, there is a risk of entering into a hyperthermic state. Hyperthermia causes an increased production of dangerous reactive oxygen species (ROS) that often lead to cell damage. ROS are free radicals that attack electron rich molecules. Methionine, a common amino acid in proteins, is especially susceptible to oxidation by ROS. The oxidized methionine can be restored to normal functionality by reduction through the activity of methionine sulfoxide reductase (Msr). Msr is a highly conserved enzyme from bacteria to humans. The gene is an antioxidant defense that reverses oxidative damage created by ROS by a reduction process through two enzymes: MsrA and MsrB. MsrA and MsrB reduce the two enantiomers of methionine sulfoxide back to functional methionine. In this study, I used RNA interference (RNAi) to knock down expression of either MsrA or MsrB to better understand the role of these genes in response to hyperthermia. Results have shown that knockdown of MsrB expression in all tissues leads to a higher failure rate in older aged flies. However, specific knockdown of MsrB in just motor neurons did not show this effect. When the flies were aged to 5 days and 24 days, knockdown of MsrB did not prove to be detrimental as flies had the same failure rates as wild type. However, when aged to 35 days the flies began to increase in failure rates. Currently, the molecular basis of MsrB is unknown. The reduced thermotolerance may be attributed to increase levels of ROS, hence MsrB’s anti-oxidative function may contribute to hyperthermic tolerance.


Keywords


Drosophila melanogaster; Msr; Thermal Stress; Methionine Sulfoxide Reductase; MsrB

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