Sickle Cell Hemoglobin

Abstract

Sickle cell hemoglobin (HbS) is an example of a genetic variant of human hemoglobin where a point mutation in the β globin gene results in substitution of glutamic acid to valine at sixth position of the β globin chain. Association between tetrameric hemoglobin molecules through noncovalent interactions between side chain residue of βVal6 and hydrophobic grooves formed by βAla70, βPhe85 and βLeu88 amino acid residues of another tetramer followed by the precipitation of the elongated polymer leads to the formation of sickle-shaped RBCs in the deoxygenated state of HbS. There are multiple non-covalent interactions between residues across intra- and inter-strands that stabilize the polymer. The clinical phenotype of sickling of RBCs manifests as sickle cell anemia, which was first documented in the year 1910 in an African patient. Although the molecular reason of the disease has been understood well over the decades of research and several treatment procedures have been explored to date, an effective therapeutic strategy for sickle cell anemia has not been discovered yet. Surprisingly, it has been observed that the oxy form of HbS and glutathionylated form of deoxy HbS inhibits polymerization. In addition to describe the residue level interactions in the HbS polymer that provides its stability, here we explain the mechanism of inhibition in the polymerization of HbS in its oxy state. Additionally, we reported the molecular insights of inhibition in the polymerization for glutathionyl HbS, a posttranslational modification of hemoglobin, even in its deoxy state. In this chapter we briefly consider the available treatment procedures of sickle cell anemia and propose that the elevation of glutathionylation of HbS within RBCs, without inducing oxidative stress, might be an effective therapeutic strategy for sickle cell anemia.

Keywords: Glutathionyl sickle hemoglobin; Hydrogen/deuterium exchange mass spectrometry; Oxygen dissociation curve; Polymerization; Sickle cell anemia; Sickle cell hemoglobin.