Crystallization and preliminary X-ray structural studies of hemoglobin A2 and hemoglobin E, isolated from the blood samples of β-thalassemic patients

Hemoglobin A2 (α2δ2), a minor (2-3%) component of circulating red blood cells, acts as an anti-sickling agent and its elevated concentration in β-thalassemia is a useful clinical diagnostic. In β-thalassemia major, where there is a failure of β-chain production, HbA2 acts as the predominant oxygen deliverer. Hemoglobin E, is another common abnormal hemoglobin, caused by splice site mutation in exon 1 of β globin gene, when combines with β-thalassemia, causes severe microcytic anemia. The purification, crystallization, and preliminary structural studies of HbA2 and HbE are reported here. HbA2 and HbE are purified by cation exchange column chromatography in presence of KCN from the blood samples of individuals suffering from β-thalassemia minor and Eβ-thalassemia. X-ray diffraction data of HbA2 and HbE were collected upto 2.1 and 1.73 A, respectively. HbA2 crystallized in space group P21 with unit cell parameters a=54.33 A, b=83.73 A, c=62.87 A, and β=99.80 degree sign whereas HbE crystallized in space group P212121 with unit cell parameters a=60.89 A, b=95.81 A, and c=99.08 A. Asymmetric unit in each case contains one Hb tetramer in R2 state