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740 a.a.
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739 a.a.
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80 a.a.
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138 a.a.
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69 a.a.
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141 a.a.
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38 a.a.
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41 a.a.
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46 a.a.
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151 a.a.
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31 a.a.
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29 a.a.
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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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Three-Dimensional structure of cyanobacterial photosystem i at 2.5 a resolution.
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Authors
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P.Jordan,
P.Fromme,
H.T.Witt,
O.Klukas,
W.Saenger,
N.Krauss.
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Ref.
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Nature, 2001,
411,
909-917.
[DOI no: ]
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PubMed id
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Abstract
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Life on Earth depends on photosynthesis, the conversion of light energy from the
Sun to chemical energy. In plants, green algae and cyanobacteria, this process
is driven by the cooperation of two large protein-cofactor complexes,
photosystems I and II, which are located in the thylakoid photosynthetic
membranes. The crystal structure of photosystem I from the thermophilic
cyanobacterium Synechococcus elongatus described here provides a picture at
atomic detail of 12 protein subunits and 127 cofactors comprising 96
chlorophylls, 2 phylloquinones, 3 Fe4S4 clusters, 22 carotenoids, 4 lipids, a
putative Ca2+ ion and 201 water molecules. The structural information on the
proteins and cofactors and their interactions provides a basis for understanding
how the high efficiency of photosystem I in light capturing and electron
transfer is achieved.
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Figure 1.
Figure 1: Structural model of PS I trimer at 2.5 Å resolution.
a, View along the membrane normal from the stromal side. For
clarity, stromal subunits have been omitted. Different
structural elements are shown in each of the three monomers (I,
II and III). I, arrangement of the transmembrane  -helices
(cylinders). Subunits are labelled. The transmembrane -helices
of PsaA (blue) and PsaB (red) are named A-a to A-k (B-a to B-k)
from the N to the C terminus (capital letters omitted). All loop
regions of PsaA and PsaB are named according to the
transmembrane helices which they connect. For all other subunits
the -helices
and  -sheets
are numbered in alphabetical order from the N to the C terminus.
Six helices in extra-membranous loop regions are drawn as
spirals. II, membrane-intrinsic subunits. In addition to the
transmembrane -helices
of the stromal and lumenal loop regions are shown in ribbon
representation. III, complete set of cofactors shown with the
transmembrane -helices
(the side chains of the antenna Chla molecules have been
omitted). Electron transfer chain: quinones and chlorophylls in blue, iron and
sulphur atoms of the three Fe[4]S[4] clusters as orange and
yellow spheres, respectively. Antenna system: chlorophylls in
yellow, carotenoids in black, lipids in turquoise. b, Side view
of the arrangement of all proteins in one monomer of PSI
(colours as in a), including the stromal subunits PsaC (pink),
PsaD (turquoise), PsaE (green) and the Fe[4]S[4] clusters. View
direction indicated by arrow at monomer II in a. The vertical
line (right) shows the crystallographic C[3] axis. c, View as in
a showing stromal subunits PsaC, PsaD and PsaE. They cover some
of the loop regions and helices of PsaA and PsaB (light grey).
Dashed ellipse: putative docking site of ferredoxin, covering
loops of PsaA.
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Figure 2.
Figure 2: Cofactors of the electron transfer chain (ETC) and of
PsaC. View parallel to the membrane plane. The pairs of
chlorophylls of the ETC are arranged in two branches A and B.
They are labelled eC, followed by the letter A or B indicating
whether PsaA or PsaB, respectively, coordinates Mg2+, and by
numbers 1 to 3 starting from the lumenal side. Phylloquinones
are Q[K]-A and Q[K]-B. The Fe[4]S[4] clusters are labelled F[X],
F[A] and F[B] according to their spectroscopic terms. The
centre-to-centre distances between the cofactors (black lines)
are given in Å. In PsaC, parts analogous to 2[Fe[4]S[4]]
bacterial ferredoxins are pink, an insertion and extensions at
C and N termini are green.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2001,
411,
909-917)
copyright 2001.
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Secondary reference #1
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Title
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Photosystem I, An improved model of the stromal subunits psac, Psad, And psae.
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Authors
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O.Klukas,
W.D.Schubert,
P.Jordan,
N.Krauss,
P.Fromme,
H.T.Witt,
W.Saenger.
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Ref.
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J Biol Chem, 1999,
274,
7351-7360.
[DOI no: ]
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PubMed id
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Figure 5.
Fig. 5. a, stereo view of PsaE including the surrounding
electron density. b, superposition of (i) NMR model from
Synechococcus sp. PCC7002 (N[S], C[S]; black) (12) and (ii)
x-ray structural model (gray) of PsaE from S. elongatus (N[SE],
C[SE]) as modeled into the present electron density map. This
figure was produced using BobScript (47).
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Figure 8.
Fig. 8. View parallel to the membrane plane of the region
assigned to PsaF, PsaJ, and PsaM. The previously unreported  -helices
y[1] and y[2] are membrane-integral. They are, however, inclined
by ~45° to the membrane normal and do not span the thylakoid
membrane. The stromal end of y[1] is located close to PsaE. This
figure was produced using BobScript (47).
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The above figures are
reproduced from the cited reference
with permission from the ASBMB
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Secondary reference #2
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Title
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Localization of two phylloquinones, Qk and qk', In an improved electron density map of photosystem i at 4-A resolution.
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Authors
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O.Klukas,
W.D.Schubert,
P.Jordan,
N.Krau,
P.Fromme,
H.T.Witt,
W.Saenger.
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Ref.
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J Biol Chem, 1999,
274,
7361-7367.
[DOI no: ]
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PubMed id
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Figure 2.
Fig. 2. The core of the reaction center of PSI. a, view
direction perpendicular to the C[2](AB)-axis onto median plane
of all cofactors of the electron transfer system. The palisade
of -helices
surrounding the electron transfer system and the loops
connecting these -helices
are rendered in black and gray. The luminal loop i-j could not
unambiguously be located in the electron density map. The
naphthalene backbone of the modeled phylloquinone orientation as
well as all remaining cofactors of the electron transfer system
are depicted in white. b, view direction from the stromal side
onto the membrane plane. The pseudo-C[2](AB)-axis passes through
the center of the Fe[4]S[4] cluster F[X]. For clarity, only the
stromal loop region j-k coordinating the iron sulfur cluster
F[X]is shown. This figure was produced using Setor (37).
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Figure 4.
Fig. 4. Schematic representations of the electron
transfer system. a, cofactor distribution along the membrane
normal showing distances in Å and fractional distances.
The observed center-to-center distances (±1 Å) (b)
and the edge-to-edge distances (±2 Å) (c) are
indicated. Except for the interplane distance between eC[1] and
eC[1]' (3.6 Å) the values of the other edge-to-edge
distances have been determined with an accuracy of 0.5 Å.
d, the individual distances and angles between the cofactors
eC[1], eC[1]', Q[K], and Q[K]' are shown. They correspond to the
center of the phylloquinones and are independent of the
phylloquinone plane orientations. Present distances and angles
are largely in agreement with those published previously (4).
Note the schematic nature of these diagrams; true distances are
supplied but may not be measured directly.
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The above figures are
reproduced from the cited reference
with permission from the ASBMB
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Secondary reference #3
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Title
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Photosystem I of synechococcus elongatus at 4 a resolution: comprehensive structure analysis.
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Authors
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W.D.Schubert,
O.Klukas,
N.Krauss,
W.Saenger,
P.Fromme,
H.T.Witt.
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Ref.
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J Mol Biol, 1997,
272,
741-769.
[DOI no: ]
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PubMed id
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Figure 4.
Figure 4. (a) View from the stromal side. The PSI trimer is
approximately discoidal, monomers being separated by lateral
indentations. The maximal distance from the C[3] axis to the
peripheral surface is  vert,
similar 105 (±5) Å. Membrane-integral subunits are
indicated in white; the subunits of the stromal ridge are
indicated in colour: PsaC, yellow, PsaD, red; PsaE, blue. The
binding pocket for ferredoxin/flavodoxin, formed by PsaC, PsaD,
PsaE and a-helix e' of either PsaA or PsaB, on the side of the
ridge distal from the C[3]-axis is indicated; asterisk: crystal
contact. (b) View along the membrane plane, i.e. view as in (a)
but flipped about the horizontal through 90°. (Produced
using Grasp; [Nicholls et al 1991].)
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Figure 9.
Figure 9. (a) Stereographic view of all 86 Chla molecules
presently identified, seen from the stromal side. Chla are
modelled as porphyrin structures, indicating their positions and
planar orientations. The region occupied by the core antenna
system largely lies within an elliptical, open-cylindrical
region. It is located between the inner reaction centre and the
outer delimiting ring of α-helices composed of the N-terminal
of the large subunits PsaA and PsaB and those of the smaller
membrane integral subunits PsaI, PsaL, PsaM, PsaJ and PsaF (see
shaded region in Figure 5). The Chla of the electron transfer
system are coloured red and connecting Chla light blue. Pink
Chla are conspicuously oriented and arranged as closely spaced
Chla pairs. (b) An analytical description of the antenna system
Chla distribution plotting the inclination (relative to the
membrane normal) of each porphyrin plane against its relative
membrane depth. The membrane-integral region is divided into a
lumenal (bottom), a middle and a stromal third, while porphyrin
plane inclinations are grouped into the categories strongly (0
to 30°, left), moderately (30 to 60°, central) and
weakly aligned (60 to 90°, right) with the membrane normal.
The number of Chla in each region (including Image but excluding
all eC) is indicated near the right-hand side of the field,
horizontal and vertical summations being indicated on the
right-hand side and at the top of the Figure (further discussion
see the text.).
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The above figures are
reproduced from the cited reference
with permission from Elsevier
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Secondary reference #4
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Title
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Photosystem I at 4 a resolution represents the first structural model of a joint photosynthetic reaction centre and core antenna system.
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Authors
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N.Krauss,
W.D.Schubert,
O.Klukas,
P.Fromme,
H.T.Witt,
W.Saenger.
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Ref.
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Nat Struct Biol, 1996,
3,
965-973.
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PubMed id
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