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Confirmation of a unique intra‐dimer cooperativity in the human hemoglobin α 1 β 1 half‐oxygenated intermediate supports the symmetry rule model of allosteric regulation
Author(s) -
Ackers Gary K.,
Holt Jo M.,
Huang Yingwen,
Grinkova Yelena,
Klinger Alexandra L.,
Denisov Ilia
Publication year - 2000
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/1097-0134(2000)41:4+<23::aid-prot30>3.0.co;2-d
Subject(s) - cooperativity , tetramer , chemistry , allosteric regulation , dimer , cooperative binding , crystallography , ligand (biochemistry) , stereochemistry , context (archaeology) , hemoglobin , binding site , biochemistry , biology , receptor , organic chemistry , enzyme , paleontology
The contribution of the α 1 β 1 half‐oxygenated tetramer [αβ:αO 2 βO 2 ] (species 21) to human hemoglobin cooperativity was evaluated using cryogenic isoelectric focusing. The cooperative free energy of binding, reflecting O 2 ‐driven protein structure changes, was measured as 21 Δ G c = 5.1 ± 0.3 kcal for the Zn/FeO 2 analog. For the Fe/FeCN analog, 21 Δ G c was estimated as 4.0 kcal after correction for a CN ligand rearrangement artifact, demonstrating that ligand rearrangement does not invalidate previous conclusions regarding this species. In the context of the entire Hb cooperativity cascade, which includes eight intermediate species, the 21 tetramer is highly abundant relative to the other doubly‐ligated species, providing strong support for the previously determined consensus partition function of O 2 binding and for the Symmetry Rule model of hemoglobin cooperativity (Ackers et al., Science 1992;255:54–63). Cooperativity of normal human hemoglobin is shown to depend on site‐configuration, and not solely the number of O 2 bound, nor the occupancy of α vs. β subunits. Verification of a unique contribution from the α 1 β 1 doubly‐oxygenated species to the equilibrium O 2 binding curve strongly reinforces the Symmetry Rule interpretation that the α 1 β 1 dimer acts both as a structural and functional element in cooperative O 2 binding. Proteins 2000;41:23–43. © 2000 Wiley‐Liss, Inc.