Human deoxyhaemoglobin-2,3-diphosphoglycerate complex low-salt structure at 2.5 A resolution

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Hemoglobin (Hb) is crucial for oxygen transport.
• 2,3-diphosphoglycerate (2,3-DPG) allosterically modulates Hb-oxygen affinity.
• Understanding the Hb-2,3-DPG complex structure is vital for deciphering oxygen homeostasis.

Purpose of the Study:

• To determine the high-resolution structure of the hemoglobin-2,3-diphosphoglycerate complex crystallized under low-salt conditions.
• To compare the low-salt structure with the previously solved high-salt structure.
• To elucidate the molecular interactions governing 2,3-DPG binding to hemoglobin.

Main Methods:

• X-ray crystallography was employed to solve the structure of the hemoglobin-2,3-diphosphoglycerate complex.
• Crystals were grown from low-salt solutions.
• The structure was determined at 2.5 Angstrom resolution.

Main Results:

• The low-salt structure exhibits significant differences compared to the high-salt structure.
• A notable loss of symmetry was observed in the 2,3-DPG binding site.
• Both lysine residues at position 82 of the beta-globin chains simultaneously interact with 2,3-DPG, forming two contacts each.

Conclusions:

• The observed structural features, particularly the enhanced lysine interactions, provide a molecular basis for the functional behavior of natural hemoglobin mutants affecting 2,3-DPG binding.
• These findings refine our understanding of allosteric regulation in hemoglobin.
• The study highlights the influence of salt concentration on the quaternary structure and ligand binding of hemoglobin.