Hemoglobin subunit alpha (HBA) within Hemoglobin S tetramer (HbS)

Hemoglobin S (HbS) is the pathological hemoglobin variant responsible for sickle cell disease, resulting from a point mutation in the beta-globin gene. The functional HbS molecule is a heterotetramer consisting of two normal alpha-globin subunits and two mutant beta-globin subunits (StatPearls, 2023). While the mutation resides in the beta chain, the alpha subunit serves as a critical therapeutic docking site for small molecules. Specifically, drugs like Voxelotor bind to the N-terminal alpha-globin chain, stabilizing hemoglobin in its oxygenated state (Oxbryta FDA Label, 2019). This allosteric modulation increases oxygen affinity, which prevents the deoxygenated HbS from polymerizing into the rigid fibers that cause red blood cell sickling (Vichinsky et al., 2019, NEJM). The resulting reduction in sickling helps prevent vaso-occlusive crises and chronic hemolytic anemia. Targeting the alpha subunit within the HbS tetramer addresses the primary molecular mechanism of sickle cell pathogenesis by maintaining the solubility of the hemoglobin molecules. This approach represents a significant shift from symptomatic treatment to disease-modifying therapy in sickle cell disease management.

Other names

Sickle hemoglobinHBA1HBA2Alpha-globinHemoglobin alpha chain

Allosteric modulation of hemoglobin to increase oxygen affinity and stabilize the oxyhemoglobin (R-state) conformation, thereby inhibiting the polymerization of deoxygenated Hemoglobin S (Vichinsky et al., 2019, NEJM).