Structural and Functional Characterization of a New Double Variant Haemoglobin (HbG-Philadelphia/Duarteα268Asn→Lysβ262Ala

Abstract

We report the first case of cosegregation of two haemoglobins (Hbs): HbG-Philadelphia [α68(E17)Asn → Lys] and HbDuarte [β62(E6)Ala → Pro]. The proband is a young patient heterozygous also for β°-thalassaemia. We detected exclusively two haemoglobin variants: HbDuarte and HbG-Philadelphia/Duarte. Functional study of the new double variant HbG-Philadelphia/Duarte exhibited an increase in oxygen affinity, with a slight decrease of cooperativity and Bohr effect. This functional behaviour is attributed to β62Ala → Pro instead of α68Asn → Lys substitution. Indeed, HbG-Philadelphia isolated in our laboratory from blood cells donor carrier for this variant is not affected by any functional modification, whereas purified Hb Duarte showed functional properties very similar to the double variant. NMR and MD simulation studies confirmed that the presence of Pro instead of Ala at the β62 position produces displacement of the E helix and modifications of the tertiary structure. The substitution α68(E17)Asn → Lys does not cause significant structural and dynamical modifications of the protein. A possible structure-based rational of substitution effects is suggested.

Complex Interaction of Hb Q-Thailand with α and β Thalassemia in a Hakka Family

“…It commonly appears with a leftward single αglobin gene deletion (-α 4.2 ). The heterozygotes of HbQ-Thailand may show minor clinical symptoms or may be asymptomatic, whereas the double heterozygosity of it and thalassemia may lead to several clinical diseases [6,7]. However, there have been few reports regarding the interaction between HbQ-Thailand and other globin gene disorders.…”