Function
Hemoglobin A is an oxygen-transport protein. Hemoglobin is also an allosteric protein. It is a tetrameter composed of two types of sub units designated α and β, with stoichiometry α2β2
The function of Hemoglobin is to carry oxygen from the lungs to the other parts of the body . Hemoglobin also help to carry carbon dioxide through the blood cells.Hemoglobin A which is a component of the red blood cells also help with the transportation of carbon dioxide and hydrogen ions to the lungs. Hemoglobin proteins are capable of carrying four molecules of Oxygen . Hemoglobin also help red blood cells to maintain their disc like shape , which allows them to move freely through the blood vessels. Each sub-unit of Hemoglobin A contains a heme prosthetic group. The heme molecules give hemoglobin its red color.[1]
Disease
The most well-known disease caused by mutation in the hemoglobin A protein is sickle-cell anemia. Sickle-cell anemia results from a mutation of the sixth residue in the β hemoglobin monomer from glutamic acid to a valine. This hemoglobin variant is termed 'hemoglobin S' (2hbs).
Relevance
Most of the understanding that of human physiology and pathology come from laboratory research that were performed on Hemoglobin.
Structural highlights
The α chain heme pocket with the relative orientation of the proximal Hisα87 and the distal Hisα58.proximal Hisα87(F8) is closer to the heme Fe atom by 0.10 Å more in the T-state compare to the R-state.[2]
The β chain heme pocket with the proximal Hisβ92(F8) and the distal Hisβ63(E7). In the R-state the proximal Hisβ92(F8) reorients itself to a more symmetric position relative to the heme molecule. In the T-state, the distal histidine E7 residue is positioned such that it partially blocks the oxygen-binding site. During the R → T transition, Hisβ63(E7) aligns itself with the heme Fe, and the Fe-His distances increase by a small but detectable amount[3]
