A new beta-chain haemoglobin variant with increased oxygen affinity: Hb Roma [beta 115(g17)Ala -> Val]

Background: Haemoglobin Roma [beta 115(G17)Ala -> Val] is a new adult haemoglobin variant found in a patient presenting a mild hypochromia and microcytosis. We studied this previously uncharacterised variant in order to evaluate the effect on the structural and funcional properties of the Ala -> Val substitution at the alpha 1 beta 1 interface. Methods and results: The variant chain was identified by direct DNA sequencing of the p-globin gene, which revealed a G (C) under barC,G (T) under barC mutation in codon 115. This mutation was confirmed by mass spectrometric analysis of the tetramers and peptides. The oxygen-binding properties of the haemoglobin A/haemoglobin Roma mixture, in which the variant makes up 25% of the haemoglobins, showed a significant increase in oxygen affinity with respect to normal haemoglobin A, both in the absence and presence of 2,3-bisphosphoglycerate. The role of the beta G-17 position, situated at the alp, interface, has been examined using computational models of haemoglobin Roma and other known beta G17 variants, in comparison with normal haemoglobin A. Conclusions: This study suggests that the 13115(G17)Ala -> Val substitution at the alpha 1 beta 1 interface is responsible for increased oxygen affinity and mild destabilisation of the haemoglobin Roma. General significance: An amino acid substitution at the G17 position of the alpha 1 beta 1 interface may result in stabilisation of the high affinity R-state of the haemoglobin molecule.