What is the structural difference between beta and gamma globin chains of Hb?

Question

Hemoglobins are tetramers composed of pairs of two different polypeptide subunits. The subunit composition of the principal hemoglobins are α2β2 (HbA; normal adult hemoglobin), α2γ2 (HbF; fetal hemoglobin) and α2δ2 (HbA2; a minor adult hemoglobin)

The total number of amino acids in beta chain and gamma chain is the same-146. The higher affinity of HbF to oxygen is due to presence of serine(in gamma chain) in place of histidine(in beta chain), which inhibits its binding with 2,3-bisphosphoglyceric acid.

Is this the only difference, or are there more such differences in the amino acid sequence?

Answer 1

Here's a pairwise sequence alignment of the human hemoglobin beta (HBB) and gamma (HBG1) chains:

HBB_HUMAN          1 VHLTPEEKSAVTALWGKVNVDEVGGEALGRLLVVYPWTQRFFESFGDLST     50
                     .|.|.|:|:.:|:|||||||::.|||.|||||||||||||||:|||:||:
HBG1_HUMAN         1 GHFTEEDKATITSLWGKVNVEDAGGETLGRLLVVYPWTQRFFDSFGNLSS     50

HBB_HUMAN         51 PDAVMGNPKVKAHGKKVLGAFSDGLAHLDNLKGTFATLSELHCDKLHVDP    100
                     ..|:||||||||||||||.:..|.:.|||:||||||.|||||||||||||
HBG1_HUMAN        51 ASAIMGNPKVKAHGKKVLTSLGDAIKHLDDLKGTFAQLSELHCDKLHVDP    100

HBB_HUMAN        101 ENFRLLGNVLVCVLAHHFGKEFTPPVQAAYQKVVAGVANALAHKYH    146
                     |||:|||||||.|||.||||||||.|||::||:|..||:||:.:||
HBG1_HUMAN       101 ENFKLLGNVLVTVLAIHFGKEFTPEVQASWQKMVTAVASALSSRYH    146

You can see the H143S (or S143H?) substitution, as well as many more.