Crystallographic, molecular modeling, and biophysical characterization of the valine{sup {beta}67} (E11) {yields} threonine variant of hemoglobin
- Univ. of Maryland Biotechnology Institute, Rockville, MD (United States)
The crystal structure of the mutant deoxyhemoglobin in which the {beta}-globin Val{sup 67}(E11) has been replaced with threonine has been determined at 2.2 {angstrom} resolution. Prior to the crystal structure determination, molecular modeling indicated that the Thr{sup 67}(E11) side chain hydroxyl group in the distal {beta}-heme pocket forms a hydrogen bond with the backbone carbonyl of His{sup 63}(E7) and is within hydrogen-bonding distance of the N{sup {delta}} of His{sup 63}(E7). The mutant crystal structure indicates only small changes in conformation in the vicinity of the E11 mutation confirming the molecular modeling predictions. Comparison of the structures of the mutant {beta}-subunits and recombinant porcine myoglobin with the identical mutation indicates similar conformations of residues in the distal heme pocket, but there is no water molecule associated with either of the threonines of the {beta}-subunits. The introduction of threonine into the distal heme pocket, despite having only small perturbations in the local structure, has a marked affect on the interaction with ligands. In the oxy derivative there is a 2-fold decrease in O{sub 2} affinity, and the rate of autoxidation is increased by 2 orders of magnitude. In the CO derivative the IR spectrum shows modifications with respect to that of normal human hemoglobin, suggesting the presence of multiple CO conformers. In the nitrosyl derivative an interaction with the O{sup {gamma}} atom of Thr{sup 67}(E11) is probably responsible for the 10-fold increase in the rate of NO release from the {beta}-subunits. In the aquomet derivative there is a 6-fold decrease in the rate of hemin dissociation suggesting an interaction of the Fe-coordinated water with the O{sup {gamma}} of Thr{sup 67}(E11). 51 refs., 6 figs., 5 tabs.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 494247
- Journal Information:
- Biochemistry (Eaton), Journal Name: Biochemistry (Eaton) Journal Issue: 6 Vol. 35; ISSN 0006-2960; ISSN BICHAW
- Country of Publication:
- United States
- Language:
- English
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