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PDBsum entry 2ig3
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Oxygen storage/transport
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PDB id
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2ig3
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References listed in PDB file
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Key reference
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Title
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Structural determinants in the group III truncated hemoglobin from campylobacter jejuni.
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Authors
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M.Nardini,
A.Pesce,
M.Labarre,
C.Richard,
A.Bolli,
P.Ascenzi,
M.Guertin,
M.Bolognesi.
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Ref.
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J Biol Chem, 2006,
281,
37803-37812.
[DOI no: ]
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PubMed id
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Abstract
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Truncated hemoglobins (trHbs) constitute a distinct lineage in the globin
superfamily, distantly related in size and fold to myoglobin and monomeric
hemoglobins. Their phylogenetic analyses revealed that three groups (I, II, and
III) compose the trHb family. Group I and II trHbs adopt a simplified globin
fold, essentially composed of a 2-on-2 alpha-helical sandwich, wrapped around
the heme group. So far no structural data have been reported for group III
trHbs. Here we report the three-dimensional structure of the group III trHbP
from the eubacterium Campylobacter jejuni. The 2.15-A resolution crystal
structure of C. jejuni trHbP (cyano-met form) shows that the 2-on-2 trHb fold is
substantially conserved in the trHb group III, despite the absence of the
Gly-based sequence motifs that were considered necessary for the attainment of
the trHb specific fold. The heme crevice presents important structural
modifications in the C-E region and in the FG helical hinge, with novel surface
clefts at the proximal heme site. Contrary to what has been observed for group I
and II trHbs, no protein matrix tunnel/cavity system is evident in C. jejuni
trHbP. A gating movement of His(E7) side chain (found in two alternate
conformations in the crystal structure) may be instrumental for ligand entry to
the heme distal site. Sequence conservation allows extrapolating part of the
structural results here reported to the whole trHb group III.
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Figure 2.
FIGURE 2. A comparative view of the trHb fold in the three
groups. A, a ribbon stereo view of Cj-trHbP tertiary structure.
 -Helices are labeled
according to the conventional globin fold nomenclature (25). B,
structural overlay of group III Cj-trHbP (blue trace) onto group
I C. eugametos trHbN (orange trace). C, structural overlay of
group III Cj-trHbP (blue trace) onto group II B. subtilis trHbO
(yellow trace). The heme groups of each globin are included. All
figures were drawn with Molscript (33) and Raster3D (34).
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Figure 3.
FIGURE 3. Structure in the heme pocket of Cj-trHbP. A, a
stereo view of the heme, of the proximal His(F8), and of the
surrounding distal residues contacting the heme and stabilizing
the bound cyanide. Hydrogen bonds within the distal residue
cluster, including the heme ligand, are indicated with dashed
lines. Residue His^46(E7) is shown in the closed and open
(magenta) conformations. B, details of the heme distal site,
including the C helix (top in the figure) and the E helix; for
comparison, the C-E backbone region of group I C. eugametos
trHbN (orange) is also displayed.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2006,
281,
37803-37812)
copyright 2006.
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