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PDBsum entry 1vhb
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Oxygen transport
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PDB id
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1vhb
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Unusual structure of the oxygen-Binding site in the dimeric bacterial hemoglobin from vitreoscilla sp.
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Authors
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C.Tarricone,
A.Galizzi,
A.Coda,
P.Ascenzi,
M.Bolognesi.
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Ref.
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Structure, 1997,
5,
497-507.
[DOI no: ]
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PubMed id
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Abstract
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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 coli 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 alpha-helical conformation, thus locating Gln53(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 A
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.
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Figure 5.
Figure 5. A structural overlay of one VtHb subunit (red)
onto the 1-272 region of Alcaligenes flavoHb, comprising the
heme domain (green) and the FAD-binding region in the C-terminal
domain (dark green). For clarity, only the heme group of VtHb is
shown, and the NADP-binding region of flavoHb (residues 273-403)
is not shown. The adenine portion of FAD (yellow) in the upper
part of the picture, points towards the CE regions of flavoHb
(yellow) and towards the 9-residue disordered CE segment of
VtHb. (The figure was drawn using the program MOLSCRIPT [68].)
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1997,
5,
497-507)
copyright 1997.
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