Unusual structure of the oxygen-binding site in the dimeric bacterial hemoglobin from Vitreoscilla sp.

Cataldo Tarricone, Alessandro Galizzi, Alessandro Coda, Paolo Ascenzi, Martino Bolognesi

Research output: Contribution to journalArticlepeer-review

Abstract

Background: The first hemoglobin identified in bacteria was isolated from Vitreoscilla stercoraria (VtHb) as a homodimeric species. The wild-type protein has been reported to display medium oxygen affinity and cooperative ligand-binding properties. Moreover, VtHb can support aerobic growth in Escherichia coil with impaired terminal oxidase function. This ability of VtHb to improve the growth properties of E. coli has important applications in fermentation technology, assisting the overexpression of recombinant proteins and antibiotics. Oxygen binding heme domains have been identified in chimeric proteins from bacteria and yeast, where they are covalently linked to FAD- and NAD(P)H-binding domains. We investigate here the fold, the distal heme site structure and the quaternary assembly of a bacterial hemoglobin which does not bear the typical flavohemoglobin domain organization. Results: The VtHb three-dimensional structure conforms to the well known globin fold. Nevertheless, the polypeptide segment connecting helices C and E is disordered, and residues E7-E10 (defined according to the standard globin fold nomenclature) do not adopt the usual α-helical conformation, thus locating GIn53(E7) out of the heme pocket. Binding of azide to the heme iron introduces substantial structural perturbations in the heme distal site residues, particularly Tyr29(B10) and Pro54(E8). The quaternary assembly of homodimeric VtHb, not observed before within the globin family, is based on a molecular interface defined by helices F and H of both subunits, the two heme iron atoms being 34 Å apart. Conclusions: The unusual heme distal site structure observed shows that previously undescribed molecular mechanisms of ligand stabilization are operative in VtHb. The polypeptide chain disorder observed in the CE region indicates a potential site of interaction with the FAD/NADH reductase partner, in analogy with observations in the chimeric flavohemoglobin from Alcaligenes eutrophus.

Original languageEnglish
Pages (from-to)497-507
Number of pages11
JournalStructure
Volume5
Issue number4
Publication statusPublished - 1997

Keywords

  • bacterial hemoglobin
  • nonvertebrate globin structure
  • oxygen-binding heme domains
  • Vitreoscilla sp. hemoglobin

ASJC Scopus subject areas

  • Molecular Biology
  • Structural Biology

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