Short insertion in a hemoglobin chain: Hb Esch, an unstable alpha1 variant with duplication of the sequence Ala65-Leu-Thr-Asn68.

Hemoglobin (Hb) Esch, is an alpha1 variant, expressed at less than 5%, resulting from the duplication of the 12 nucleotides corresponding to CD65 through 68. The effect of this insertion is the repetition of the sequence Ala-Leu-Thr-Asn, which corresponds to the last turn of helix E. In this variant the presence of a one-turn elongated helix E causes instability and increased ligand affinity. Hb Esch was characterized by DNA sequencing and confirmed by electrospray mass spectrometry. Functional studies were performed by flash photolysis measurements on a fraction isolated by flatbed isoelectric focusing, which was enriched in the abnormal hemoglobin. Similar to other alpha chain variants due to short insertion (or deletion), Hb Esch probably results from a slipped mispairing mechanism. The stability of such modified proteins depends upon the region which is added or deleted and usually is more stable when involving a flexible loop or complete helix turn(s) near by.

New alpha 2 globin chain variant with low oxygen affinity affecting the N-terminal residue and leading to N-acetylation [Hb Lyon-Bron alpha 1(NA1)Val --> Ac-Ala].

Hemoglobin Lyon-Bron was found in two members of a family of German ascent presenting with a moderate normocytic anemia. In this alpha 2 globin variant, the N-terminal valine of the chain was replaced by an alanine. Electrospray mass spectrometry of the alpha chain showed that, as normally, the initiator methionine was cleaved during globin processing but that the N alpha-terminal group was totally acetylated. This resulted in structural modifications of a region crucial for oxygen binding. As a consequence, hemoglobin Lyon-Bron displayed both a reduced chloride effect and a decreased oxygen affinity, this last point explaining the apparent anemia.