Which of the following is required in the formation of the structure of Haemoglobin?

The Beta-chain of Hb begins with valine and histidine. Both these amino acids are impoant in the synthesis and structure of heamoglobin. Alignment according to helical designation makes homology evident: Residue F8 is the proximal heme-linked histidine, and the histidine on the distal side of the heme is E7. The iron atom is linked by a coordinate bond to the imidazole nitrogen (N) of histidine F8. The E7 distal histidine, on the other side of the heme plane, is not bonded to the iron atom but is very close to the ligand-binding site. Ref: Natarajan K., Townes T.M., Kutlar A. (2010). Chapter 48. Disorders of Hemoglobin Structure: Sickle Cell Anemia and Related Abnormalities. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e