title: Reversible hexacoordination of alpha-hemoglobin-stabilizing protein (AHSP)/alpha-hemoglobin Versus pressure. Evidence for protection of the alpha-chains by their chaperone.
abstract: Using high hydrostatic pressure or hydrogen peroxide as perturbing agents, we demonstrate a protective effect of the chaperone AHSP for the alpha-chains of Hb. High pressure induces an irreversible aggregation of the ferrous deoxy alpha-chains, whereas the AHSP/alpha-Hb complex shows reversible hexacoordination of the alpha-Hb without protein aggregation. Upon pressure release, the relaxation kinetics of the transition from the hexacoordinated to pentacoordinated form of alpha-Hb in the presence of AHSP exhibit a biphasic shape. High pressure did not induce dissociation of alpha-Hb from its chaperone, as evidenced by the ligand binding kinetics that show a unique rate for the AHSP/alpha-Hb complex. For both free alpha-Hb and the AHSP/alpha-Hb complex, the bimolecular rate constant of CO binding (k(CO)(on)) versus pressure exhibits a bell shape, attributed to the transition of the rate-determining step from the chemical barrier to the migration of CO within the protein matrix. These results reveal a plasticity of the alpha-Hb active site in the presence of the chaperone and indicate that the AHSP was still active at 300 MPa. The ferric state of the AHSP/alpha-Hb complex shows hexacoordination even at atmospheric pressures, indicating a His-Fe-His binding scheme as previously observed in neuroglobin and cytoglobin. The reaction with hydrogen peroxide of ferric alpha-Hb within the complex also demonstrates a protection against aggregation.
authors.affiliation: INSERM U779, University of Paris XI, 94275 Le Kremlin-Bicêtre, France.
authors.forename: Djemel
authors.initials: D
authors.lastname: Hamdane
authors.forename: Corinne
authors.initials: C
authors.lastname: Vasseur-Godbillon
authors.forename: Véronique
authors.initials: V
authors.lastname: Baudin-Creuza
authors.forename: Gaston Hui Bon
authors.initials: GH
authors.lastname: Hoa
authors.forename: Michael C
authors.initials: MC
authors.lastname: Marden
mesh_terms: D001798:Blood Proteins / Q000502:physiology*; D002248:Carbon Monoxide / Q000378:metabolism; D019281:Dimerization; D006454:Hemoglobins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006874:Hydrostatic Pressure; D007700:Kinetics; D018832:Molecular Chaperones / Q000502:physiology*; D044367:Phase Transition
chemical_list: C468768:AHSP protein, human; D001798:Blood Proteins; D006454:Hemoglobins; D018832:Molecular Chaperones; D002248:Carbon Monoxide; D006861:Hydrogen Peroxide