The structure of greylag goose oxy haemoglobin: the roles of four mutations compared with bar-­headed goose haemoglobin

The greylag goose (Anser anser), which lives on lowlands and cannot tolerate hypoxic conditions, presents a striking contrast to its close relative the bar-headed goose (A. indicus), which lives at high altitude and possesses high-altitude hypoxia adaptation. There are only four amino-acid residue differences at α18, α63, α119 and β125 between the haemoglobins of the two species. The crystal structure of greylag goose oxy haemoglobin was determined at 3.09 Å resolution. Its quaternary structure is slightly different from that of the bar-headed goose oxy haemoglobin, with a rotation of 2.8° in relative orientation of the two dimers. Of the four mutations, those at α119 and β125 produce contact changes in the α₁β₁ interface and may be responsible for the differences in intrinsic oxygen affinity between the two species; those at α18 and α63 may be responsible for the differences in quaternary structure between the two species.