Hemoglobin (Hb) E (beta26 Glu6Lys) is the most common worldwide abnormal hemoglobin (Hb) variant. Homozygotes for HbE present a benign clinical picture with mild anemia. When combined with beta-thalassemia, it becomes a severe hemoglobinopathy most prevalent in Southeast Asia, but now encountered with increasing frequency in immigrants in the United States. Little research emphasis has been applied in our country to HbE in spite of the growing number of immigrants with these diseases. Mechanisms that give rise to the pathophysiology stemming from the interaction of HbE with beta-thalassemia have not been adequately explained or elucidated. At the molecular level, HbE exhibits normal oxygen binding but decreased stability. The beta26 Lys substitution is distant from the heme pocket, which may account for the normal oxygen affinity. However, its increased instability may be due to its location near the alpha1beta1 interface. Our preliminary molecular modeling indicates that the heightened instability could result from the disruption and weakening of hydrogen bonds across the alpha1beta1 interface. This could result in increased dissociation and a greater propensity for oxidation and hemichrome formation to explain increased oxidative damage in HbE/ a thalassemia red cell membranes. Others proposed that instability may only play a role during febrile episodes because of the thermal instability of HbE. Thus, there is still a need to resolve the role of HbE instability in the pathogenesis. To date, there is no high-resolution HbE crystal structure or details of the alterations and conformational changes, nor is there an animal model for EE disease and E/beta-thalassemia.
The aims of this proposal are to obtain the high resolution structure of HbE by crystallography/molecular modeling, and generate a transgenic animal model for HbE and HbE-Thalassemia for purposes of resolving mechanisms of this disease at the molecular, red blood cell, and organ levels. These studies will set the stage for future R01 applications with long-term goals of designing/testing therapeutic approaches in the transgenic mouse model; and to elucidate the mechanism of innate resistance to malaria provided by HbE.
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