The globins are the protein products of a large and ancient multigene family, including the alpha and beta globins of hemoglobin, myoglobin, and even the leghemoglobins of plants. The common function of the globins is to bind oxygen. The sequences represented here are all beta globins.
Functional hemoglobin contains two molecules each of the alpha and beta globin chains.
The juxtaposition of the four chains, each of which can bind an oxygen molecule, allows hemoglobin to adjust its oxygen-binding capacity according to the oxygen concentration of its environment. It is beta globin that is altered in human sickle-cell anemia and thalassemia. In sickle-cell anemia only one amino acid of 146 has been altered, while in thalassemia, the amino acid sequence is terminated prematurely. Both alterations lead to changes in folding pattern that severely alter the function of the molecule. In the normal folding pattern the six helical regions of the molecule are folded into a single compact domain.