Meeting Abstract
The loss of expression of the oxygen-binding protein hemoglobin (Hb) in Antarctic icefishes (suborder Notothenioidei, family Channichthyidae) is considered by most to be a neutral mutation, persisting in icefishes inhabiting the icy-cold and oxygen-rich waters of the Southern Ocean where competition is minimal. The lack of expression of the intracellular oxygen-binding protein myoglobin (Mb) in cardiac muscle is more of a conundrum. Mutations leading to the loss of Mb occurred at four points during the radiation of the icefish family and by three distinct molecular mechanisms, suggesting weak selective pressure maintaining the Mb gene. Both Hb and Mb are iron-centered proteins that can promote the formation of reactive oxygen species and elevate oxidative stress. Moreover, the potential for oxidative damage may be particularly high in notothenioids, due to their high capacities for oxidative metabolism, membranes rich in polyunsaturated fatty acids, and oxygen-rich environment. We investigated whether the loss of Hb and Mb may be advantageous to icefishes because it reduces oxidative stress, thereby reducing rates of protein turnover and resulting in an energetic costs savings. Despite having higher levels of oxidized and ubiquitinated proteins, red-blooded and red-hearted notothenioids do not synthesize or degrade proteins at a faster rate than icefishes, and energy expenditures on protein synthesis are equivalent between the two groups. These data support the idea that the losses of Hb and Mb are disaptations. Research supported by NSF (OPP 1341663).
