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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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