Hemoglobin Einstein: semisynthetic deletion in the B-helix of the alpha-chain

A Novel α2-Globin Gene Mutation: Hb Debao [α31(B12)Arg→Trp; HBA2: c.94A>T]

We report a novel mutation on the α2-globin gene, Hb Debao [α31(B12)Arg→Trp; HBA2: c.94A>T] detected in a Chinese family. This mutation gives rise to a previously undescribed hemoglobin (Hb) variant that was undetectable by electrophoretic or chromatographic methods. Hb Debao was associated with an α⁺-thalassemia (α⁺-thal) deletion [-α^3.7 (rightward)] producing a mild phenotype with significant microcytosis and hypochromia, while the combination of this mutation with an α⁰-thal deletion (--^SEA) resulting in a severe form of Hb H (β4) disease, which is consistent with a thalassemic phenotype associated with the novel mutation.

Pair-wise interactions of polymerization inhibitory contact site mutations of hemoglobin-S

The linkage of pair-wise interactions of contact site mutations of HbS has been studied using Le Lamentin [His-20 (alpha)-->Gln], Hoshida [Glu-43 (beta)-->Gln] and alpha(2)beta (2) (T87Q) mutations as the prototype of three distinct classes of contact sites of deoxy HbS fiber. Binary mixture experiments established that beta(A)-chain with the Thr-87 (beta)-->Gln mutation is as potent as the gamma-chain of HbF (alpha(2)gamma(2)) in inhibiting polymerization. On combining the influence of Le Lamentin mutation with that of beta (2) (T87Q) mutations; the net influence is only partial additivity. On the other hand, in binary mixture studies, combined influence of Hoshida mutation with that of beta (2) (T87Q) mutations is synergistic. Besides, a significant level of synergistic complementation is also seen when the Le Lamentin and Hoshida mutations are combined in HbS (symmetrical tetramers). Le Lamentin and Hoshida mutation introduced into the cis-dimer of the asymmetric hybrid tetramer completely neutralizes the Val-6 (beta) dependent polymerization. Accordingly, we propose that combining the perturbation of intra-double strand contact site with that of an inter-double strand contact site exhibit synergy when they are present in two different chains of the alphabeta dimer. A comparison of the present results with that of the earlier studies suggest that when the two contact site perturbations are from the same sub-unit of the alphabeta dimer only partial additivity is observed. The map of interaction linkage of the contact site mutations exposes new strategies in the design of novel anti-sickling Hbs for the gene therapy of sickle cell disease.