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Crystal structure of Lysbeta(1)82-Lysbeta(2)82 crosslinked hemoglobin: a possible allosteric intermediate
E J Fernandez1, C Abad-Zapatero, K W Olsen
1Department of Chemistry, Loyola University Chicago, Chicago, IL 60626, USA.
Journal of Molecular Biology
|March 4, 2000
Summary
This study determined the crystal structure of crosslinked human hemoglobin (HbA), revealing an intermediate state between oxygenated (R) and deoxygenated (T) conformations. This crosslinked HbA exhibits high oxygen affinity and altered cooperativity due to structural stabilization.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Crystallography
Background:
- Human hemoglobin (HbA) undergoes significant conformational changes between its high-affinity oxy R-state and low-affinity deoxy T-state.
- Allosteric regulation of HbA involves complex structural transitions crucial for oxygen transport.
- Understanding these transitions is key to comprehending hemoglobinopathies and developing therapeutic strategies.
Purpose of the Study:
- To elucidate the structural basis of altered oxygen affinity and cooperativity in a chemically modified human hemoglobin.
- To determine the crystal structure of human hemoglobin crosslinked at the Lysbeta82 residues.
- To investigate the conformational state of crosslinked hemoglobin under deoxy conditions.
Main Methods:
- X-ray crystallography was employed to determine the three-dimensional structure.
- Human hemoglobin was chemically modified using bis(3,5-dibromosalicyl) fumarate under oxy conditions.
- Crystallization and structural analysis were performed under deoxy conditions at 2.30 Å resolution.
Main Results:
- The crystal structure of Lysbeta82-crosslinked human hemoglobin (beta82XLHbA) was determined.
- The modified hemoglobin exhibits increased oxygen affinity and lacks cooperativity.
- The structure displays intermediate conformational characteristics between the R and T-states, with R-state-like features in the distal Hisbeta63 position.
- Key allosteric regions, including Tyrbeta145 and the switch region, are in intermediate positions.
Conclusions:
- The Lysbeta82 crosslink stabilizes an intermediate conformation of hemoglobin, hindering a full transition to the T-state.
- The R-state-like positioning of distal Hisbeta63 likely contributes to the high oxygen affinity of beta82XLHbA.
- The structure represents a stabilized intermediate in the allosteric transition of hemoglobin, offering insights into protein conformational dynamics.