Table of Contents
ISRN Hematology
Volume 2011, Article ID 735314, 10 pages
http://dx.doi.org/10.5402/2011/735314
Research Article

Structural and Functional Characterization of a New Double Variant Haemoglobin (HbG-Philadelphia/Duarte 𝛼 𝟔 𝟖 A s n L y s 𝟐 𝛽 𝟔 𝟐 A l a P r o 𝟐 )

1Department of Sciences Applied to Biosystems, University of Cagliari, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato, Italy
2Department of Chemical Sciences, University of Cagliari, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato, Italy
3SLACS, Istituto Officina dei Materiali del CNR and Department of Physics, University of Cagliari, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato, Italy
4Department of Biomedical and Biotecnologies Sciences, University of Cagliari, via Jenner, 09121 Cagliari, Italy

Received 8 September 2010; Accepted 4 October 2010

Academic Editors: J. S. Gibson, T. Ikuta, and D. Lavelle

Copyright © 2011 Antonella Fais et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We report the first case of cosegregation of two haemoglobins (Hbs): HbG-Philadelphia [ 𝛼 6 8 ( E 1 7 ) A s n L y s ] and HbDuarte [ 𝛽 6 2 ( E 6 ) A l a P r o ]. 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 𝛽 6 2 A l a P r o instead of 𝛼 6 8 A s n L y s 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 𝛽 6 2 position produces displacement of the E helix and modifications of the tertiary structure. The substitution 𝛼 6 8 ( E 1 7 ) A s n L y s does not cause significant structural and dynamical modifications of the protein. A possible structure-based rational of substitution effects is suggested.