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PDBsum entry 2q2h
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References listed in PDB file
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Key reference
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Title
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Phage display and crystallographic analysis reveals potential substrate/binding site interactions in the protein secretion chaperone csaa from agrobacterium tumefaciens.
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Authors
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A.R.Feldman,
Y.A.Shapova,
S.S.Wu,
D.C.Oliver,
M.Heller,
L.P.Mcintosh,
J.K.Scott,
M.Paetzel.
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Ref.
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J Mol Biol, 2008,
379,
457-470.
[DOI no: ]
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PubMed id
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Abstract
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The protein CsaA has been proposed to function as a protein secretion chaperone
in bacteria that lack the Sec-dependent protein-targeting chaperone SecB. CsaA
is a homodimer with two putative substrate-binding pockets, one in each monomer.
To test the hypothesis that these cavities are indeed substrate-binding sites
able to interact with other polypeptide chains, we selected a peptide that bound
to CsaA from a random peptide library displayed on phage. Presented here is the
structure of CsaA from Agrobacterium tumefaciens (AtCsaA) solved in the presence
and absence of the selected peptide. To promote co-crystallization, the sequence
for this peptide was genetically fused to the amino-terminus of AtCsaA. The
resulting 1.65 A resolution crystal structure reveals that the tethered peptide
from one AtCsaA molecule binds to the proposed substrate-binding pocket of a
symmetry-related molecule possibly mimicking the interaction between a
pre-protein substrate and CsaA. The structure shows that the peptide lies in an
extended conformation with alanine, proline and glutamine side chains pointing
into the binding pocket. The peptide interacts with the atoms of the
AtCsaA-binding pocket via seven direct hydrogen bonds. The side chain of a
conserved pocket residue, Arg76, has an "up" conformation when the CsaA-binding
site is empty and a "down" conformation when the CsaA-binding site is occupied,
suggesting that this residue may function to stabilize the peptide in the
binding cavity. The presented aggregation assays, phage-display analysis and
structural analysis are consistent with AtCsaA being a general chaperone. The
properties of the proposed CsaA-binding pocket/peptide interactions are compared
to those from other structurally characterized molecular chaperones.
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Figure 1.
Fig. 1. The structure of AtCsaA. (a) A ribbon diagram of
dimeric AtCsaA, with molecule A in green and molecule B in pink.
(b) A C^α-trace diagram of the superimposed structures of
AtCsaA (green), BsCsaA (2NZH, red), and TtCsaA (1GD7, blue).
Circles represent areas of the CsaA molecule with high thermal
motion. (c) A surface representation of the AtCsaA structure
colored according to the negative (red), positive (blue), or
neutral (white) electrostatic potential. The location of the
putative binding site is indicated with arrows.
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Figure 3.
Fig. 3. Structure of the bound peptide from the
X15peptide–AtCsaA complex. An electron density omit map
calculated for the tethered peptide in the CsaA-binding pocket,
contoured at 1 sigma.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2008,
379,
457-470)
copyright 2008.
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