Hemoglobin Einstein: Semisynthetic deletion in the B-helix of the α-chain

The influence of the deletion of the tetra peptide segment α _23-26 of the B-helix of the ot-chain of hemoglobin-A on its assembly, structure, and functional properties has been investigated. The hemoglobin with the deletion, ss-Hemoglobin-Einstein, is readily assembled from semisynthetic α_1-141des_23-26 globin and human β^A-chain. The deletion of α_23-26 modulates the O₂ affinity of hemoglobin in a buffer/allosteric effector specific fashion, but has little influence on the Bohr effect. The deletion has no influence on the thermodynamic stability of the α₁β ₁ and the α₁β₂ interface. The semisynthetic hemoglobin exhibits normal intersubunit interactions at the α₁β₁ and α₁β₂ interfaces as reflected by ¹H-NMR spectroscopy. Molecular modeling studies of ss-Hemoglobin-Einstein suggest that the segment α _28-35 is in a helical conformation, while the segment α _19-22 is the nonhelical AB region. The shortened B-helix conserves the interactions of α₁β₁ interface. The results demonstrate a high degree of plasticity in the hemoglobin structure that accommodates the deletion of α_23-26 without perturbing its overall global conformation.