ATP regulation of the ligand-binding properties in temperate and cold-adapted haemoglobins. X-ray structure and ligand-binding kinetics in the sub-Antarctic fish Eleginops maclovinus

The major haemoglobin of the sub-Antarctic fish Eleginops maclovinus was structurally and functionally characterised with the aim to compare molecular environmental adaptations in the O-2-transport system of sub-Antarctic fishes of the suborder Notothenioidei with those of their high-latitude relatives. Ligand-binding kinetics of the major haemoglobin of E. maclovinus indicated strong stabilisation of the liganded quaternary T state, enhanced in the presence of the physiological allosteric effector ATP, compared to that of high-Antarctic Trematomus bernacchii. The activation enthalpy for O-2 dissociation was dramatically lower than that in T. bernacchii haemoglobin, suggesting remarkable differences in temperature sensitivity and structural changes associated with O-2 release and exit from the protein. The haemoglobin functional properties, together with the X-ray structure of the CO form at 1.49 angstrom resolution, the first of a temperate notothenioid, strongly support the hypothesis that in E. maclovinus, whose life-style varies according to changes in habitat, the mechanisms that regulate O-2 affinity and the ATP-induced Root effect differ from those of high-Antarctic Notothenioids.