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PDBsum entry 1bvb
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Electron transport
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PDB id
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1bvb
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References listed in PDB file
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Key reference
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Title
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Heme packing motifs revealed by the crystal structure of the tetra-Heme cytochrome c554 from nitrosomonas europaea.
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Authors
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T.M.Iverson,
D.M.Arciero,
B.T.Hsu,
M.S.Logan,
A.B.Hooper,
D.C.Rees.
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Ref.
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Nat Struct Biol, 1998,
5,
1005-1012.
[DOI no: ]
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PubMed id
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Abstract
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Cytochrome c554 (cyt c554), a tetra-heme cytochrome from Nitrosomonas europaea,
is an essential component in the biological nitrification pathway. In N.
europaea, ammonia is converted to hydroxylamine, which is then oxidized to
nitrite by hydroxylamine oxidoreductase (HAO). Cyt c554 functions in the latter
process by accepting pairs of electrons from HAO and transferring them to a
cytochrome acceptor. The crystal structure of cyt c554 at 2.6 A resolution shows
a predominantly alpha-helical protein with four covalently attached hemes. The
four hemes are arranged in two pairs such that the planes of the porphyrin rings
are almost parallel and overlapping at the edge; corresponding heme arrangements
are observed in other multi-heme proteins. Striking structural similarities are
evident between the tetra-heme core of cyt c554 and hemes 3-6 of HAO, which
suggests an evolutionary relationship between these redox partners.
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Figure 1.
Figure 1. The oxidation of NH[3] to NO[2]^− by Nitrosomonas
europaea. Ammonia is first oxidized to hydroxylamine
(NH[2]OH) by ammonia monooxygenase (AMO.) The product, NH[2]OH,
is oxidized to NO[ 2]^− by HAO. The released electrons are
transferred to cyt c554 (a two electron acceptor) and then
possibly to cyt c552 (a one electron acceptor), which ultimately
passes electrons to terminal oxidases. The electron transfer
pathway following the oxidation of NH[2]OH to NO[2]^− is not
fully understood and alternative electron transfer routes may
exist^30, including the transfer of electrons from cyt c554
directly to a membrane-bound electron transport chain^31.
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Figure 3.
Figure 3. Heme configuration and superposition of heme stacking
motifs. a, Inter-heme iron distances and overall heme
configuration. Hemes are shown in the same view as in Fig. 2a.
b, Overlay of hemes I and III from cyt c554 (red) with hemes 1
and 2 from HAO (teal), hemes 3 and 5 from HAO (magenta), hemes 6
and 7 from HAO (green) and hemes 1 and 2 from the split Soret
cytochrome (yellow). The pseudo two-fold axis has been
calculated for the hemes of cyt c554 and is shown as a black
line. c, Overlay of hemes II and IV from cyt c554 (red) with
P460 and 6 of HAO (teal). The 5-coordinate hemes II (cyt c554)
and P460 (HAO) are on the right. The pseudo two-fold axis
calculated for hemes II and IV of cyt c554 is indicated as a
black line. d, Overlay of the two central hemes, hemes III and
IV, from cyt c554 with hemes 5 and 6 from HAO (teal), hemes 7
and 8 from HAO (green), hemes 69 and 70 from cyt c551.5
(magenta) and hemes 201 and 203 from cyt c[3] (yellow). e,
Stereoview of the overlay of all hemes and surrounding
structural elements from cyt c554 (red) with hemes 3−6 of HAO
(teal).
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nat Struct Biol
(1998,
5,
1005-1012)
copyright 1998.
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