title: Polar bear hemoglobin and human Hb A0: same 2,3-diphosphoglycerate binding site but asymmetry of the binding?
abstract: Polar bear (Ursus maritimus) hemoglobin (Hb) shows a low response to 2,3-diphosphoglycerate (2,3-DPG), compared to human Hb A0, even though these proteins have the same 2,3-DPG-binding site. In addition, polar bear Hb shows a high response to chloride and an alkaline Bohr effect (deltalog P50/deltapH) that is significantly greater than that of human Hb A0. The difference in sequence Pro (Hb A0)-->Gly (polar bear Hb) at position A2 in the A helix seems to be critical for reduced binding of 2,3-DPG. Our results also show that the A2 position may influence not only the flexibility of the A helix, but that differences in flexibility of the first turn of the A helix may affect the unloading of oxygen for the intrinsic ligand affinities of the alpha and beta chains. However, preferential binding to either chain can only take place if there is appreciable asymmetric binding of the phosphoric effector. Regarding this point, 31P NMR data suggest a loss of symmetry of the 2,3-DPG-binding site in the deoxyHb-2,3-DPG complex.
authors.affiliation: Istituto di Biochimica, Università Cattolica Sacro Cuore, Facoltà di Medicina A. Gemelli Largo F. Vito 1, 00168 Roma, Italia. m.pomponi@rm.unicatt.it
authors.forename: Massimo
authors.initials: M
authors.lastname: Pomponi
authors.forename: Claudia
authors.initials: C
authors.lastname: Bertonati
authors.forename: Maria
authors.initials: M
authors.lastname: Patamia
authors.forename: Maurizio
authors.initials: M
authors.lastname: Marta
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Derocher
authors.forename: Christian
authors.initials: C
authors.lastname: Lydersen
authors.forename: Kit M
authors.initials: KM
authors.lastname: Kovacs
authors.forename: Oystein
authors.initials: O
authors.lastname: Wiig
authors.forename: Astrid J
authors.initials: AJ
authors.lastname: Bårdgard
mesh_terms: D019794:2,3-Diphosphoglycerate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002712:Chlorides / Q000737:chemistry; D006441:Hemoglobin A / Q000737:chemistry* / Q000378:metabolism*; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D011485:Protein Binding; D001503:Ursidae / Q000097:blood*
chemical_list: D002712:Chlorides; D006454:Hemoglobins; D019794:2,3-Diphosphoglycerate; C028881:hemoglobin A(0); D006441:Hemoglobin A