Reversible hexacoordination of alpha-hemoglobin-stabilizing protein (AHSP)/alpha-hemoglobin Versus pressure. Evidence for protection of the alpha-chains by their chaperone.
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.
Hamdane
Djemel
D
INSERM U779, University of Paris XI, 94275 Le Kremlin-Bicêtre, France.
Vasseur-Godbillon
Corinne
C
Baudin-Creuza
Véronique
V
Hoa
Gaston Hui Bon
GH
Marden
Michael C
MC
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
C468768:AHSP protein, human; D001798:Blood Proteins; D006454:Hemoglobins; D018832:Molecular Chaperones; D002248:Carbon Monoxide; D006861:Hydrogen Peroxide