Importance of helices A and H in oxygen binding differences between bovine and human hemoglobins.
Human and bovine hemoglobins (Hbs) exhibit several functional differences. They have a similar oxygen affinity in the presence of 2,3-diphosphoglycerate (2,3-DPG); however, bovine Hb has a greatly diminished 2,3-DPG effect, which itself is chloride dependent. The question is to determine whether these differences have a common structural origin, or whether they evolved in an independent fashion. The decreased 2,3-DPG effect can be partially reproduced by mutations at the effector binding sites, substituting the betaNA1 valine-NA2 histidine present in human Hb with a methionine. While changes of human Hb at these sites could provoke the bovine characteristic of the lower 2,3-DPG effect, the oxygen affinities of these mutated Hbs were not as low as that of the bovine Hb. Modifications responsible for tertiary structural modifications of helix A in human Hb might help shift the N-terminal methionine position, thereby locking helix A in place. We replaced the residues proline beta5(A2), arginine beta104(G6), and tyrosine beta130(H8) of human Hb by the residues present in bovine beta-globin, namely alanine, lysine, and phenylalanine, respectively. These mutations did not allow us to obtain a low oxygen affinity recombinant Hb (rHb). This indicates that other factors also influence oxygen binding and the effects are only partially coupled.
Baudin-Creuza
Véronique
V
Institut National de la Santé et de la Recherche Médicale Unité 473, 84, rue du Général Leclerc, 94276 Le Kremlin-Bicêtre, France. baudin@kb.inserm.fr
Vasseur-Godbillon
Corinne
C
Kister
Jean
J
Domingues
Elisa
E
Poyart
Claude
C
Marden
Michael
M
Pagnier
Josée
J
D000328:Adult; D019943:Amino Acid Substitution / Q000235:genetics / Q000502:physiology; D000818:Animals; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D002417:Cattle; D019281:Dimerization; D004588:Electrophoresis, Cellulose Acetate / Q000379:methods; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D016297:Mutagenesis, Site-Directed / Q000235:genetics / Q000502:physiology; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D011489:Protein Denaturation; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D006454:Hemoglobins; D011994:Recombinant Proteins; D010100:Oxygen