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Fig. 1
Protein composition, electron micrographs and 3D analysis of the
PSII supercomplex.
a, SDS-PAGE of the PSII-enriched membranes (track 1) and
PSII supercomplex (track 2), stained with Coomassie R250. b
and c are cryoelectron micrographs of a typical preparation
of the PSII supercomplex showing particles randomly orientated in
vitreous ice, under focused at 1.35 mm and 7.2 mm, respectively.
d, Selection of typical class averages used for the 3D reconstruction.
e, Reprojections of the 3D map in identical orientations
with the corresponding class averages.
f, Surface representation of the final 3D map viewed in the
same orientation as the class averages.
Fig. 2
3D map of the PSII supercomplex at 24 Å and sections 10 Å thick
through the map.
a, Half the 3D map, corresponding to a single dimeric supercomplex,
is viewed from an oblique angle to visualise the lumenal surface
and the extrinsic OEC proteins labelled A/A` (assigned to 33 kDa
OEC protein) and B/B` (assigned to 23 kDa and 17 kDa OEC proteins).
The putative location of the membrane-spanning region is indicated.
Also shown are the overall dimensions, including the maximum extent
of the protrusions corresponding to the OEC extrinsic proteins.
b, Surface representation of the 3D map indicating 10 Å thick
sections taken as follows:
c, Projection map of the transmembrane region towards the
stromal surface.
d, Projection map of the region close to the lumenal surface.
e, Projection map of the region occupied by the OEC extrinsic
proteins.
Fig. 3
Positioning of major transmembrane helices of the central dimeric
core region within the PSII supercomplex.
a, Projection map obtained from 2D crystals of the PSII core
dimer complex at 9 Å showing proposed positions of its transmembrane
helices taken from Hankamer et al.(13)
The model for the D1 and D2 proteins shown in yellow and orange,
respectively, was constructed using the coordinates for the L and
M subunits of R. viridis (17)
as justified by a recent 8 Å 3D structure of the PSII CP47 RC complex
(15). The 6 red helices in
each monomer correspond to those of CP47 and the corresponding 2
fold related 6 green helices are those of CP43. The additional 7
transmembrane helices colored in purple were identified in Rhee
et al.(15) and are unknown
low molecular weight proteins.
b, Superimposition of the transmembrane helices determined
by electron crystallography (13,15)
onto a projection from the 3D reconstruction of the core complex
from a subpopulation of 1,100 particles identified by cryoelectron
microscopy (estimated resolution 32 Å).
c, Superimposition of the transmembrane helices in a and
b onto a projection map obtained from the 3D reconstruction (estimated
resolution 28 Å) calculated from 3,700 particles of a subpopulation
of supercomplexes that have lost one LHCII-containing peripheral
region, thus exposing one edge of the central core dimer (also see
ref. 7).
d, Position of the core dimer transmembrane helices in the
central region of the projection map from the 3D reconstruction
of the intact supercomplex (estimated resolution 24 Å) based on
a, b and c. Projections b, c and d do not include the extrinsic
proteins.
Fig. 4
Structural model of the intrinsic protein subunits within the PSII
supercomplex.
a, b, Shows a semi-transparent surface representation
of the structural model, viewed from the side and lumenal surface
respectively, containing helices of the protein subunits based on
detailed comparison of high and intermediate resolution structures.
The positions of the transmembrane helices of the core dimer are
based on Fig. 3 and the same colour
code has been used. The LHCII, CP24 and CP26 are derived from Kühlbrandt
et al.(16) and have been positioned
based on internal density distribution in the supercomplex and on
cross-linking data (31,32).
The region flanking the central core may also contain the PsbS protein
(2) but no attempt has been
made to model this four transmembrane helical protein into the map.
The interface between the extrinsic OEC proteins and the lumenal
surface has been assumed to be at the lumenal side of slice d in
Fig. 2b and this is shown as 'windows'
looking into the intrinsic interior of the supercomplex.
c, A magnification of the docking sites for the extrinsic
OEC proteins emphasising the underlying helices of the core dimer.
The helices attributed to the D1 and D2 proteins (yellow and orange,
respectively), are modelled using the coordinates of the L and M
subunits of R. viridis as are the CD (in white) and AB (in red)
lumenal loops.
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