Question

How do Hemogloblin's amino acids dictate the structure & function of the protein? (using binding/active sites, polar/non-polar residues & catalytic mechanisms)

Answer 1

Haemoglobin structure is related to myoglobin in both it's structure and function. It reversly binds with molecular oxygen which it transports in the red corpuscles of blood rather than muscle tissue. Haemoglobin is made up of four polypeptide chains whereas in myoglobin only one polypeptide chain. Haemoglobin contains alpha chains consists of 141amino acids and beta chains consists of 146 amino acids. Each chains or subunits consists of one heme group of myoglobin. That alpha and beta chains have different affinity towards oxygen but both are useful for oxygen availability in the cell.

Proteins quaternary structure includes haemoglobin. Proteins are of two types simple one contains only amino acids and conjugated proteins contains amino acids as well as non- amino acids which is called prosthetic groups. The porphyrin group is fixed into haemoglobin and shows strong interaction between alpha and beta chains. X-ray crystallography data shown that haemoglobin exist in two major conformational state they are stressed T state and relaxed R state. The capacity of haemoglobin to bind oxygen depends upon the presence of bound prosthetic groups called heme they are called fifth and sixth coordination sites. The iron in heme binds with 4 N atom in the centre of porphyrin ring but this leaves two free binding sites for iron, one on either side of the heme plane. Heme group is located in a crevice of myoglobin molecules surrunded by non- polar residues, except for two polar histidines.

Haemoglobin dictates as protein functions helps in the transportation of CO2 and hydrogen ions back to the lungs, and able to bind with gaseous NO and O2. Hydroxylation and dealkylation reaction is catalyzed by haemoglobin. Haemoglobin can bind with protons and CO2 , which causes a conformational change in protein and facilitates the release of oxygen. Protons bind at various places on the protein, while CO2 binds with only alpha- amino group, CO2 binds with haemoglobin and forms carbinohaemoglobin.