A new beta-chain haemoglobin variant with increased oxygen affinity: Hb Roma [beta115(g17)Ala-->Val]

Background Haemoglobin Roma [\u3b2115(G17)Ala \u2192 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 \u2192 Val substitution at the \u3b11\u3b21 interface. Methods and results The variant chain was identified by direct DNA sequencing of the \u3b2-globin gene, which revealed a GCC \u2192 GTC 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 \u3b2G17 position, situated at the \u3b11\u3b21 interface, has been examined using computational models of haemoglobin Roma and other known \u3b2G17 variants, in comparison with normal haemoglobin A. Conclusions This study suggests that the \u3b2115(G17)Ala \u2192 Val substitution at the \u3b11\u3b21 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 \u3b11\u3b21 interface may result in stabilisation of the high affinity R-state of the haemoglobin molecule