Molecular characterization of novel mitochondrial peroxiredoxins from the Antarctic emerald rockcod and their gene expression in response to environmental warming.

In the present study we describe the molecular characterization of the two paralogous mitochondrial peroxiredoxins from Trematomus bernacchii, a teleost that plays a pivotal role in the Antarctic food chain. The two putative amino acid sequences were compared with orthologs from other fish, highlighting a high percentage of identity and similarity with the respective variant, in particular for the residues that are essential for the characteristic peroxidase activity of these enzymes. The temporal expression of Prdx3 and Prdx5 mRNAs in response to short-term thermal stress showed a general upregulation of prdx3, suggesting that this isoform is the most affected by temperature increase. These data, together with the peculiar differences between the molecular structures of the two mitochondrial Prdxs in T. bernacchii as well as in the tropical species Stegastes partitus, suggest an adaptation that allowed these poikilothermic aquatic vertebrates to colonize very different environments, characterized by different temperature ranges.

Peroxiredoxin 6 from the Antarctic emerald rockcod: molecular characterization of its response to warming.

In the present study, we describe the purification and molecular characterization of two peroxiredoxins (Prdxs), referred to as Prdx6A and Prdx6B, from Trematomus bernacchii, a teleost widely distributed in many areas of Antarctica, that plays a pivotal role in the Antarctic food chain. The two putative amino acid sequences were compared with Prdx6 orthologs from other fish, highlighting a high percentage of identity and similarity with the respective variant, in particular for the residues that are essential for the characteristic peroxidase and phospholipase activities of these enzymes. Phylogenetic analyses suggest the appearance of the two prdx6 genes through a duplication event before the speciation that led to the differentiation of fish families and that the evolution of the two gene variants seems to proceed together with the evolution of fish orders and families. The temporal expression of Prdx6 mRNA in response to short-term thermal stress showed a general upregulation of prdx6b and inhibition of prdx6a, suggesting that the latter is the variant most affected by temperature increase. The variations of mRNA accumulation are more conspicuous in heart than the liver, probably related to behavioral changes of the specimens in response to elevated temperature. These data, together with the peculiar differences between the molecular structures of the two Prdx6s in T. bernacchii as well as in the tropical species Stegastes partitus, suggest an adaptation that allowed these poikilothermic aquatic vertebrates to colonize very different environments, characterized by different temperature ranges.

Temperature interactions of the molecular chaperone Hsc70 from the eurythermal marine goby Gillichthys mirabilis.

Molecular chaperones participate in many aspects of protein biogenesis. Mechanistically, they recognize and bind to non-native proteins, prevent the aggregation of unfolded proteins and also, in some cases, facilitate refolding. Although a great deal is known about the cellular function of molecular chaperones in general, very little is known about the effect of temperature on molecular chaperones in non-model organisms, particularly in ectotherms that fold proteins under variable-temperature conditions in nature. To address this issue, we studied the temperature interactions of a major cytosolic molecular chaperone, Hsc70, from the eurythermal marine goby Gillichthys mirabilis. Using in vitro assays, we measured the intrinsic activity, unfolded-protein-stimulated activity, temperature sensitivity and heat stability of the ATPase activity of native Hsc70 purified from G. mirabilis white muscle. Similar to other chaperones in the 70kDa heat-shock protein family, G. mirabilis Hsc70 exhibited a low intrinsic ATPase activity that was stimulated in vitro by the addition of unfolded protein. Across the environmentally relevant temperature range (10-35 degrees C), the ATPase activity of G. mirabilis Hsc70 displayed differential thermal sensitivity, with the greatest sensitivity occurring between 10 and 15 degrees C and the least sensitivity between 15 and 25 degrees C. In addition, the activity of Hsc70 was not significantly different between the unstimulated and unfolded-protein-stimulated treatments, suggesting that the ATPase activity and the peptide-binding domain of Hsc70 have similar thermal sensitivities in vitro. Finally, the thermal stability of Hsc70 ATPase activity greatly exceeded environmental temperatures for G. mirabilis, with activity up to 62.5 degrees C. Overall, the biochemical characterization of the ATPase activity suggests that, although Hsc70 is not an extraordinarily thermally stable protein, it is capable of protein chaperoning cycles even at the extremes of environmental temperatures encountered by G. mirabilis in nature.