Structural and functional studies of hemoglobin Suresnes (arg 141 alpha 2 replaced by His beta 2). Consequences of disrupting an oxygen-linked anion-binding site.
Hb Suresnes is a human hemoglobin variant in which histidine replaces arginine at the COOH terminus of the alpha chains. The COOH-terminal arginines of the alpha chains play a major role in normal human hemoglobin (HbA), both by electrostatic interactions which constrain deoxygenated hemoglobin in a low affinity quaternary conformation and by involvement in oxygen-linked anion binding knoiwn to give rise to a large part of the alkaline Bohr effect. An x-ray crystallographic analysis of deoxyHb Suresnes reveals the loss of the normal intersubunit salt bridge to lysine 127 alpha and a decrease in the occupancy of inorganic anions at the alpha chain aniom-binding site. Relative to normal HbA, Hb Suresnes has a high affinity for oxygen, a reduced cooperativity in oxygen biding, and greatly reduced pH and chloride sensitivity. similar changes are found in carboxypeptidase B-digested hemoglobin Ao where the COOH-terminal arginine is removed by enzymatic digestion. Both equilibrium and kinetic manifestations of the destabilization of the normal low affinity configuration are observed. Inositol hexaphosphate restores cooperativity and pH sensitivity but, even in the presence of this strong allosteric effector, the low and high affinity conformations of Hb Suresnes appear to differ from those of HbA. In both the unliganded and liganded states, apreciable subunit dissociation of Hb Suresnes is apparent, which suggests that the substitution disrupts bonds which normally stabilize the tetramer. Structural changes at both the quaternary and tertiary level appear to contribute to alterations in the high and low affinity conformations of ths abnormal hemoglobin. Hb Suresnes thus illustrtaes the consequences of the loss of an important oxygen-linked anion-binding site.
Poyart, C; Bursaux, E; Arnone, A; Bonaventura, J; Bonaventura, C
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