Background: Haemoglobin Roma [beta115(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 alpha1beta1 interface.
Methods and results: The variant chain was identified by direct DNA sequencing of the beta-globin gene, which revealed a GCC-->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 betaG17 position, situated at the alpha(1)beta(1) interface, has been examined using computational models of haemoglobin Roma and other known betaG17 variants, in comparison with normal haemoglobin A.
Conclusions: This study suggests that the beta115(G17)Ala-->Val substitution at the alpha1beta1 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 alpha1beta1 interface may result in stabilisation of the high affinity R-state of the haemoglobin molecule.
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