The evolution of arctic fish hemoglobin protein and gene characterization

Polar fish have adapted physiologically and biochemically to survive, grow and reproduce in the cold. The capacity of fish to colonise a variety of habitats has evolved in parallel with modulation of their hemoglobin (Hb) systems at molecular/functional level. Due to less extreme and less constant climate, the Arctic ecosystem may fill an intermediate position between the Antarctic and the temperate/tropical ones. In Arctic haemoglobins, the structure/function relationship reveals important differences in comparison with Antarctic ones, indicating a distinct evolutionary pathway. Within the study of the molecular bases of cold adaptation in fish inhabiting the polar habitats, and taking advantage of the information available on haemoglobin structure and function, we analyzed the evolutionary history of the a and b globins of Antarctic and Arctic haemoglobins, as a basis for reconstructing the phylogenetic relationships among species. This communication reports the molecular and structural characterisation of the oxygen-transport system of three Gadidae: the Arctic cod Arctogadus glacialis, the polar cod Boreogadus saida and the atlantic cod Gadus morhua (all species belonging to the superorder Paracanthopterygii, order Gadiformers). Their blood was found to have three major hemoglobins (Hb 1, Hb 2, Hb 3).