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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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