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PDBsum entry 1fb0
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Electron transport
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PDB id
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1fb0
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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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Crystal structures of two functionally different thioredoxins in spinach chloroplasts.
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Authors
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G.Capitani,
Z.Marković-Housley,
G.Delval,
M.Morris,
J.N.Jansonius,
P.Schürmann.
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Ref.
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J Mol Biol, 2000,
302,
135-154.
[DOI no: ]
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PubMed id
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Abstract
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Thioredoxins are small ubiquitous proteins which act as general protein
disulfide reductases in living cells. Chloroplasts contain two distinct
thioredoxins ( f and m) with different phylogenetic origin. Both act as enzyme
regulatory proteins but have different specificities towards target enzymes.
Thioredoxin f (Trx f), which shares only low sequence identity with thioredoxin
m (Trx m) and with all other known thioredoxins, activates enzymes of the Calvin
cycle and other photosynthetic processes. Trx m shows high sequence similarity
with bacterial thioredoxins and activates other chloroplast enzymes. The here
described structural studies of the two chloroplast thioredoxins were carried
out in order to gain insight into the structure/function relationships of these
proteins. Crystal structures were determined for oxidized, recombinant
thioredoxin f (Trx f-L) and at the N terminus truncated form of it (Trx f-S), as
well as for oxidized and reduced thioredoxin m (at 2.1 and 2.3 A resolution,
respectively). Whereas thioredoxin f crystallized as a monomer, both truncated
thioredoxin f and thioredoxin m crystallized as non-covalent dimers. The
structures of thioredoxins f and m exhibit the typical thioredoxin fold
consisting of a central twisted five-stranded beta-sheet surrounded by four
alpha-helices. Thioredoxin f contains an additional alpha-helix at the N
terminus and an exposed third cysteine close to the active site. The overall
three-dimensional structures of the two chloroplast thioredoxins are quite
similar. However, the two proteins have a significantly different surface
topology and charge distribution around the active site. An interesting feature
which might significantly contribute to the specificity of thioredoxin f is an
inherent flexibility of its active site, which has expressed itself
crystallographically in two different crystal forms.
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Figure 6.
Figure 6. Superimposed stereo C^a traces of the Trx f-L
(green), Trx m (blue) and E. coli Trx (red) structures. The
active-site residues appear in ball-and-stick mode. The
active-site tryptophan 45 of Trx f-L is labelled. Prepared with
DINO [Philippsen 1998].
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Figure 9.
Figure 9. Stereo view of the superimposed Trx f-L, Trx f-S
and Trx m ball-and-stick atomic models in the active site region
centered around Asp66 (Trx m). The Trx m model is depicted in
yellow and atom colors, the Trx f-S model in green and that of
Trx f-L in magenta. Water molecules appear as red spheres. The
residues Asp66 (Trx m) and Asn74 (Trx f) are labelled, as are
Trp45 of Trx f-L (green label) and of Trx f-S (magenta label).
The hydrogen bond between Asp66 and Trp36 in Trx m, as well as
that between Asn74 and Asn77 in Trx f are drawn as light cyan
lines. Prepared with DINO [Philippsen 1998].
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2000,
302,
135-154)
copyright 2000.
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