title: Interrelationship among Fe-His Bond Strengths, Oxygen Affinities, and Intersubunit Hydrogen Bonding Changes upon Ligand Binding in the β Subunit of Human Hemoglobin: The Alkaline Bohr Effect.
abstract: Regulation of the oxygen affinity of human adult hemoglobin (Hb A) at high pH, known as the alkaline Bohr effect, is essential for its physiological function. In this study, structural mechanisms of the alkaline Bohr effect and pH-dependent O2affinity changes were investigated via1H nuclear magnetic resonance and visible and UV resonance Raman spectra of mutant Hbs, Hb M Iwate (αH87Y) and Hb M Boston (αH58Y). It was found that even though the binding of O2to the α subunits is forbidden in the mutant Hbs, the O2affinity was higher at alkaline pH than at neutral pH, and concomitantly, the Fe-His stretching frequency of the β subunits was shifted to higher values. Thus, it was confirmed for the β subunits that the stronger the Fe-His bond, the higher the O2affinity. It was found in this study that the quaternary structure of α(Fe3+)β(Fe2+-CO) of the mutant Hb is closer to T than to the ordinary R at neutral pH. The retained Aspβ94-Hisβ146 hydrogen bond makes the extent of proton release smaller upon ligand binding from Hisβ146, known as one of residues contributing to the alkaline Bohr effect. For these T structures, the Aspα94-Trpβ37 hydrogen bond in the hinge region and the Tyrα42-Aspβ99 hydrogen bond in the switch region of the α1-β2interface are maintained but elongated at alkaline pH. Thus, a decrease in tension in the Fe-His bond of the β subunits at alkaline pH causes a substantial increase in the change in global structure upon binding of CO to the β subunit.
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba , Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Shigenori
authors.identifier: 0000-0003-4753-9516
authors.initials: S
authors.lastname: Nagatomo
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba , Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Okumura
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba , Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Kazuya
authors.identifier: 0000-0001-8065-0772
authors.initials: K
authors.lastname: Saito
authors.affiliation: Picobiology Institute, Graduate School of Life Science, University of Hyogo , 3-2-1 Kouto, Kamigori, Ako-gun, Hyogo 678-1297, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ogura
authors.affiliation: Picobiology Institute, Graduate School of Life Science, University of Hyogo , 3-2-1 Kouto, Kamigori, Ako-gun, Hyogo 678-1297, Japan.
authors.forename: Teizo
authors.initials: T
authors.lastname: Kitagawa
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University , Koganei, Tokyo 184-0003, Japan.|School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University , Kanazawa, Ishikawa 920-0942, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Nagai
mesh_terms: D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry*; D006801:Humans; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism*; D000072756:Protein Conformation, alpha-Helical
chemical_list: D006454:Hemoglobins; D008024:Ligands; D006639:Histidine; D007501:Iron; D010100:Oxygen