title: An Origin of Cooperative Oxygen Binding of Human Adult Hemoglobin: Different Roles of the α and β Subunits in the α2β2 Tetramer.
abstract: Human hemoglobin (Hb), which is an α2β2 tetramer and binds four O2 molecules, changes its O2-affinity from low to high as an increase of bound O2, that is characterized by 'cooperativity'. This property is indispensable for its function of O2 transfer from a lung to tissues and is accounted for in terms of T/R quaternary structure change, assuming the presence of a strain on the Fe-histidine (His) bond in the T state caused by the formation of hydrogen bonds at the subunit interfaces. However, the difference between the α and β subunits has been neglected. To investigate the different roles of the Fe-His(F8) bonds in the α and β subunits, we investigated cavity mutant Hbs in which the Fe-His(F8) in either α or β subunits was replaced by Fe-imidazole and F8-glycine. Thus, in cavity mutant Hbs, the movement of Fe upon O2-binding is detached from the movement of the F-helix, which is supposed to play a role of communication. Recombinant Hb (rHb)(αH87G), in which only the Fe-His in the α subunits is replaced by Fe-imidazole, showed a biphasic O2-binding with no cooperativity, indicating the coexistence of two independent hemes with different O2-affinities. In contrast, rHb(βH92G), in which only the Fe-His in the β subunits is replaced by Fe-imidazole, gave a simple high-affinity O2-binding curve with no cooperativity. Resonance Raman, 1H NMR, and near-UV circular dichroism measurements revealed that the quaternary structure change did not occur upon O2-binding to rHb(αH87G), but it did partially occur with O2-binding to rHb(βH92G). The quaternary structure of rHb(αH87G) appears to be frozen in T while its tertiary structure is changeable. Thus, the absence of the Fe-His bond in the α subunit inhibits the T to R quaternary structure change upon O2-binding, but its absence in the β subunit simply enhances the O2-affinity of α subunit.
authors.affiliation: Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Shigenori
authors.initials: S
authors.lastname: Nagatomo
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Yukifumi
authors.initials: Y
authors.lastname: Nagai
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Aki
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakurai
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Kiyohiro
authors.initials: K
authors.lastname: Imai
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan; Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Mizusawa
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ogura
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Teizo
authors.initials: T
authors.lastname: Kitagawa
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan; Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan,3 School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, Japan,4 Department of Frontier Biosciences, Hosei University, Koganei, Tokyo, Japan,5 Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, Sayo, Sayo-gun, Hyogo, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Nagai
mesh_terms: D000328:Adult; D002942:Circular Dichroism; D005998:Glycine / Q000737:chemistry / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D007093:Imidazoles / Q000737:chemistry / Q000378:metabolism; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D055542:alpha-Globins / Q000737:chemistry / Q000378:metabolism; D055544:beta-Globins / Q000737:chemistry / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D007093:Imidazoles; D055542:alpha-Globins; D055544:beta-Globins; D006639:Histidine; C100003:deoxyhemoglobin; D007501:Iron; D010100:Oxygen; D005998:Glycine