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Dynamics of α-Hb chain binding to its chaperone AHSP depends on heme coordination and redox state

Abstract : Background: AHSP is an erythroid molecular chaperone of the α-hemoglobin chains (α-Hb). Upon AHSP binding, native ferric α-Hb undergoes an unprecedented structural rearrangement at the heme site giving rise to a 6th coordination bond with His(E7). Methods: Recombinant AHSP, WT α-Hb:AHSP and α-Hb(HE7Q):AHSP complexes were expressed in Escherichia coli. Thermal denaturation curves were measured by circular dichroism for the isolated α-Hb and bound to AHSP. Kinetics of ligand binding and redox reactions of α-Hb bound to AHSP as well as α-Hb release from the α-Hb:AHSP complex were measured by time-resolved absorption spectroscopy. Results: AHSP binding to α-Hb is kinetically controlled to prevail over direct binding with β-chains and is also thermodynamically controlled by the α-Hb redox state and not the liganded state of the ferrous α-Hb. The dramatic instability of isolated ferric α-Hb is greatly decreased upon AHSP binding. Removing the bis-histidyl hexacoordination in α-HbH58(E7)Q:AHSP complex reduces the stabilizing effect of AHSP binding. Once the ferric α-Hb is bound to AHSP, the globin can be more easily reduced by several chemical and enzymatic systems compared to α-Hb within the Hb-tetramer. Conclusion: α-Hb reduction could trigger its release from AHSP toward its final Hb β-chain partner producing functional ferrous Hb-tetramers. This work indicates a preferred kinetic pathway for Hb-synthesis. General significance: The cellular redox balance in Hb-synthesis should be considered as important as the relative proportional synthesis of both Hb-subunits and their heme cofactor. The in vivo role of AHSP is discussed in the context of the molecular disorders observed in thalassemia.
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https://www.hal.inserm.fr/inserm-03131771
Contributor : Véronique Baudin-Creuza <>
Submitted on : Thursday, February 4, 2021 - 4:24:11 PM
Last modification on : Saturday, February 6, 2021 - 3:30:57 AM

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Laurent Kiger, Corinne Vasseur, Elisa Domingues-Hamdi, Gilles Truan, Michael Marden, et al.. Dynamics of α-Hb chain binding to its chaperone AHSP depends on heme coordination and redox state. Biochimica et Biophysica Acta (BBA) - General Subjects, Elsevier, 2014, 1840 (1), pp.277-287. ⟨10.1016/J.BBAGEN.2013.09.015⟩. ⟨inserm-03131771⟩

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