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PDBsum entry 3deo
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Protein transport, membrane protein
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PDB id
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3deo
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References listed in PDB file
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Key reference
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Title
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Structural basis for specific substrate recognition by the chloroplast signal recognition particle protein cpsrp43.
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Authors
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K.F.Stengel,
I.Holdermann,
P.Cain,
C.Robinson,
K.Wild,
I.Sinning.
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Ref.
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Science, 2008,
321,
253-256.
[DOI no: ]
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PubMed id
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Abstract
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Secretory and membrane proteins carry amino-terminal signal sequences that, in
cotranslational targeting, are recognized by the signal recognition particle
protein SRP54 without sequence specificity. The most abundant membrane proteins
on Earth are the light-harvesting chlorophyll a/b binding proteins (LHCPs). They
are synthesized in the cytoplasm, imported into the chloroplast, and
posttranslationally targeted to the thylakoid membrane by cpSRP, a heterodimer
formed by cpSRP54 and cpSRP43. We present the 1.5 angstrom crystal structure of
cpSRP43 characterized by a unique arrangement of chromodomains and ankyrin
repeats. The overall shape and charge distribution of cpSRP43 resembles the SRP
RNA, which is absent in chloroplasts. The complex with the internal signal
sequence of LHCPs reveals that cpSRP43 specifically recognizes a DPLG peptide
motif. We describe how cpSPR43 adapts the universally conserved SRP system to
posttranslational targeting and insertion of the LHCP family of membrane
proteins.
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Figure 1.
Fig. 1. Structure of cpSRP43. (A) Scheme of the domain
structure of cpSRP43 with chromodomains (CD1 to 3) and ankyrin
repeats (Ank1 to 4). Domains present in the crystal structure
are given by residue numbers and are indicated in rainbow
colors. (B) Side view of cpSRP43 in ribbon representation. The
domains are labeled. (C) Side view of cpSRP43 [90° rotation
with respect to (B)]. Secondary structure elements are numbered.
The N- and C-termini are labeled. (D) Front view of cpSRP43. The
surface representation shows two hydrophobic grooves separated
by a positive ridge. The molecular surface is colored blue and
red according to positive and negative electrostatic potential,
respectively. The asterisk highlights Tyr^204 in Ank3. (E) Back
view of cpSRP43 [same view as in (C)] showing the highly
negatively charged surface with a spacing of negative charges
reminiscent of RNA (see fig. S2).
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Figure 2.
Fig. 2. Structure of the cpSRP43/L18p complex. (A) LHCP
topology with three transmembrane helices (TM1 to 3). The
sequence of the L18 region is given for the major LHCP, Lhcb1
from Pisum sativum, which was used in this study (red, the DPLG
motif is underlined). TM3 starts immediately after the L18
region. (B) Typical isothermal titration calorimetry (ITC)
experiment of the cpSRP43 interaction with L18p. (C) Ribbon
representation of cpSRP43 (blue) with bound L18p (as a
ball-and-stick model, gray). The N- and C-termini are indicated.
(D) Surface representation of the cpSRP43/L18p complex. The
peptide (labeled by residue numbers) binds in the hydrophobic
groove 1. Four residues at the N terminus and two residues at
the C terminus are not resolved.
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The above figures are
reprinted
by permission from the AAAs:
Science
(2008,
321,
253-256)
copyright 2008.
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