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Structure of deoxy-quaternary haemoglobin with liganded beta subunits
B Luisi1, B Liddington, G Fermi
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511.
Journal of Molecular Biology
|July 5, 1990
Summary
We determined the structure of T-state hemoglobin with bound carbon monoxide and nickel. Ligand binding in the T state mirrors quaternary transition adjustments, restricting heme movement and explaining low beta-heme affinity.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Hemoglobin (Hb) transports oxygen, exhibiting allosteric regulation.
- The T (tense) state represents Hb's low-affinity conformation.
- Understanding T-state structural dynamics is crucial for elucidating Hb's function.
Purpose of the Study:
- To determine the structure of a T-state hemoglobin with specific modifications.
- To investigate the structural consequences of ligand binding in the T state.
- To explain the mechanism behind the reduced ligand affinity in the beta subunits of T-state Hb.
Main Methods:
- X-ray crystallography was used to determine the high-resolution structure.
- Specific substitutions (nickel for heme iron in alpha subunits) and ligand binding (carbon monoxide to beta subunits) were employed.
Main Results:
- The structure of T-state hemoglobin with CO-bound beta-hemes and nickel-substituted alpha-subunits was determined.
- Structural adjustments upon ligand binding in the T state align with quaternary transition movements.
- Translational movement of the heme group is significantly restricted in this T-state conformation.
Conclusions:
- The restricted heme movement in the T state limits structural adjustments necessary for high ligand affinity.
- These findings provide a structural basis for the inherently low ligand affinity of the beta-hemes in T-state hemoglobin.
- The study elucidates key structural features governing hemoglobin's allosteric regulation.