The crystal structure of bar-headed goose hemoglobin in deoxy form: The allosteric mechanism of a hemoglobin species with high oxygen affinity

The crystal structure of a high oxygen affinity species of hemoglobin, Engi neering and Plant Genetic bar-headed goose hemoglobin in deoxy form, has be en determined to a resolution of 2.8 Angstrom. The R and R-free factor of t he model are 0.197 and Sciences, Peking University 0.243, respectively. The structure reported here is a special deoxy state of hemoglobin and indicat es the differences in allosteric mechanisms between the goose and human hem oglobins. The quaternary structure of the goose deoxy hemoglobin shows obvi ous differences from that of human deoxy hemoglobin. The rotation angle of one alpha beta dimer relative to its partner in a tetramer molecule from th e goose oxy to deoxy hemoglobin is only 4.6 degrees, and the translation is only 0.3 Angstrom, which are much smaller than those in human hemoglobin. In the alpha (1)beta (2) switch region of the goose deoxy hemoglobin, the i midazole ring of His beta (2)97 does not span the side-chain of Thr alpha ( 1)41 relative to the oxy hemoglobin as in human hemoglobin. And the tertiar y structure changes of heme pocket and FG corner are also smaller than that in human hemoglobin. A unique mutation among avian and mammalian Hbs of al pha 119 from proline to alanine at the alpha (1)beta (1) interface in bar-h eaded goose hemoglobin brings a gap between Ala alpha 119 and Leu beta 55, the minimum distance between the two residues is 4.66 Angstrom. At the entr ance to the central cavity around the molecular dyad, some residues of two beta chains form a positively charged groove where the inositol pentaphosph ate binds to the hemoglobin. The His beta 146 is at the inositol pentaphosp hate binding site and the salt-bridge between His beta 146 and Asp beta 94 does not exist in the deoxy hemoglobin, which brings the weak chloride-inde pendent Bohr effect to bar-headed goose hemoglobin. (C) 2001 Academic Press .