Assembly of human hemoglobin. Studies with Escherichia coli-expressed α-globin

Maria Teresa Sanna, Anna Razynska, Michael Karavitis, Aditya P. Koley, Fred K. Friedman, Irina M. Russu, William S. Brinigar, Clara Fronticelli

Research output: Contribution to journalArticle

Abstract

The α-globin of human hemoglobin was expressed in Escherichia call and was refolded with heme in the presence and in the absence of native β- chains. The functional and structural properties of the expressed α-chains were assessed in the isolated state and after assembly into a functional hemoglobin tetramer. The recombinant and native hemoglobins were essentially identical on the basis of sensitivity to effectors (Cl- and 2,3- diphosphaglycerate), Bohr effect, CO binding kinetics, dimer-tetramer association constants, circular dichroism spectra of the heme region, and nuclear magnetic resonance of the residues in the α1β1 and α1β2 interfaces. However, the nuclear magnetic resonance revealed subtle differences in the heme region of the expressed α-chain, and the recombinant human normal adult hemoglobin (HbA) exhibited a slightly decreased cooperativity relative to native HbA. These results indicate that subtle conformational changes in the heme pocket can alter hemoglobin cooperativity in the absence of modifications of quaternary interface contacts or protein dynamics. In addition to incorporation into a HbA tetramer, the α-globin refolds and incorporates heme in the absence of the partner β-chain. Although the CO binding kinetics of recombinant α-chains were the same as that of native α-chains, the ellipticity of the Soret circular dichroism spectrum was decreased and CO binding kinetics revealed an additional faster component. These results show that recombinant α-chain assumes alternating conformations in the absence of β-chain and indicate that the isolated α- chain exhibits a higher degree of conformational flexibility than the α- chain incorporated into the hemoglobin tetramer. These findings demonstrate the utility of the expressed α-globin as a tool for elucidating the role of this chain in hemoglobin structure-function relationships.

Original languageEnglish (US)
Pages (from-to)3478-3486
Number of pages9
JournalJournal of Biological Chemistry
Volume272
Issue number6
DOIs
StatePublished - 1997
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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    Sanna, M. T., Razynska, A., Karavitis, M., Koley, A. P., Friedman, F. K., Russu, I. M., Brinigar, W. S., & Fronticelli, C. (1997). Assembly of human hemoglobin. Studies with Escherichia coli-expressed α-globin. Journal of Biological Chemistry, 272(6), 3478-3486. https://doi.org/10.1074/jbc.272.6.3478