What is the molecular structure of Hemoglobin S?

The molecular structure of Hemoglobin S is characterized by the substitution of valine for glutamic acid at the sixth position of the beta chain. This specific change is crucial because it alters the properties of hemoglobin and can lead to sickle cell disease.

In normal adult hemoglobin (Hemoglobin A), the amino acid at the sixth position of the beta chain is glutamic acid, which is a hydrophilic molecule. When glutamic acid is replaced with valine, which is hydrophobic, this causes a change in the hemoglobin's solubility and its ability to carry oxygen. The hydrophobic valine causes the hemoglobin molecules to stick together under low oxygen conditions, leading to the characteristic sickling of red blood cells. Such sickling contributes to the symptoms of sickle cell disease, including pain and anemia.

Understanding this molecular change is essential for recognizing the pathophysiology of sickle cell disease and the consequences of Hemoglobin S on red blood cell function.