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 alpha18, alpha63, alpha119 and beta125 between the haemoglobins of the two species. The crystal structure of greylag goose oxy haemoglobin was determined at 3.09 A resolution. Its quaternary structure is slightly different from that of the bar-headed goose oxy haemoglobin, with a rotation of 2.8 degrees in relative orientation of the two dimers. Of the four mutations, those at alpha119 and beta125 produce contact changes in the alpha(1)beta(1) interface and may be responsible for the differences in intrinsic oxygen affinity between the two species; those at alpha18 and alpha63 may be responsible for the differences in quaternary structure between the two species.