THE CRYSTAL-STRUCTURE OF A HIGH OXYGEN-AFFINITY SPECIES OF HEMOGLOBIN(BAR-HEADED GOOSE HEMOGLOBIN IN THE OXY FORM)

We have determined the crystal structure of bar-headed goose haemoglob in in the oxy form to a resolution of 2.0 Angstrom. The R-factor of th e model is 19.8%. The structure is similar to human HbA, but contacts between the subunits show slightly altered packing of the tetramer. Ba r-headed goose blood shows a greatly elevated oxygen affinity compared to closely related species of geese. This is apparently due to a sing le proline to alanine mutation at the alpha(1) beta(1) interface which destabilises the T state of the protein. The beta chain N and C termi ni are well-localized, and together with other neighbouring basic grou ps they form a strongly positively charged groove at the entrance to t he central cavity around the molecular dyad. The well-ordered conforma tion and the three-dimensional distribution of positive charges clearl y indicate this area to be the inositol pentaphosphate binding site of bird haemoglobins. (C) 1996 Academic Press Limited