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X-ray diffraction studies of a partially liganded hemoglobin, [alpha(FeII-CO)beta(MnII)]2
Journal of Molecular Biology
|April 20, 1986
Summary
Hybrid hemoglobin with manganese-substituted beta subunits retains the deoxy quaternary structure (T-state) even when partially CO-liganded. CO binding causes localized T-state changes, distinct from full ligand-induced structural shifts.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Crystallography
Background:
- Hemoglobin's quaternary structure (T-state and R-state) is crucial for cooperative oxygen binding.
- Understanding structural changes upon partial ligand binding is key to elucidating cooperativity mechanisms.
Purpose of the Study:
- To analyze the structural consequences of partial ligand binding in a mixed-metal hybrid hemoglobin.
- To compare structural changes in the T-state upon partial CO binding versus full ligand binding.
Main Methods:
- Single-crystal X-ray diffraction at 3.0 Å resolution.
- Analysis of a hybrid hemoglobin with alpha(FeII-CO) and beta(MnII) subunits.
Main Results:
- The manganese-substituted beta subunits are structurally identical to normal deoxy beta subunits.
- Carbon monoxide binding to alpha subunits induces localized T-state structural changes.
- These changes involve movement of the alpha-heme iron and the F helix, differing from full ligand-induced shifts.
Conclusions:
- Partial ligand binding in the T-state results in localized structural adjustments, not the major quaternary shifts seen in fully liganded hemoglobin.
- Findings provide insights into stereochemical theories of cooperative ligand binding and the Bohr effect.