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PDBsum entry 2co7
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Fibril protein
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PDB id
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2co7
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References listed in PDB file
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Key reference
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Title
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Donor-Strand exchange in chaperone-Assisted pilus assembly proceeds through a concerted beta strand displacement mechanism.
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Authors
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H.Remaut,
R.J.Rose,
T.J.Hannan,
S.J.Hultgren,
S.E.Radford,
A.E.Ashcroft,
G.Waksman.
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Ref.
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Mol Cell, 2006,
22,
831-842.
[DOI no: ]
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PubMed id
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Abstract
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Gram-negative pathogens commonly use the chaperone-usher pathway to assemble
adhesive multisubunit fibers on their surface. In the periplasm, subunits are
stabilized by a chaperone that donates a beta strand to complement the subunits'
truncated immunoglobulin-like fold. Pilus assembly proceeds through a
"donor-strand exchange" (DSE) mechanism whereby this complementary beta strand
is replaced by the N-terminal extension (Nte) of an incoming pilus subunit.
Using X-ray crystallography and real-time electrospray ionization mass
spectrometry (ESI-MS), we demonstrate that DSE requires the formation of a
transient ternary complex between the chaperone-subunit complex and the Nte of
the next subunit to be assembled. The process is crucially dependent on an
initiation site (the P5 pocket) needed to recruit the incoming Nte. The data
also suggest a capping reaction displacing DSE toward product formation. These
results support a zip-in-zip-out mechanism for DSE and a catalytic role for the
usher, the molecular platform at which pili are assembled.
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Figure 4.
Figure 4. Kinetics of DSE
ESI-MS data showing (A) the
decline of the initial SafB-SafA[Ntd2] complex, (B) the
appearance of the SafA[Ntd2]-A[Nte] product, (C) the release of
free SafB, and (D) the decline in concentration of the ternary
SafB-SafA[Ntd2]-A[Nte] complex. Either wt A[Nte] (dark blue)
or different variant peptides (F17A, green; I15A, light blue;
V13A, orange; or F3A, magenta) were used to initiate the
reaction. A control experiment in which no peptide was added is
shown in (A) as a red dotted line. See the Supplemental Data for
normalization procedure.
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Figure 7.
Figure 7. Model for the Mechanism of DSE In Vitro and In Vivo
(A) Schematic representation of DSE in vitro. Chaperone and
subunit are labeled (i) and (ii), respectively. In the
chaperone, strands G[1] and F[1] are represented as solid black
lines. In the subunit, strand F, which directly interacts with
the G[1] donor strand, is depicted in blue. An incoming Nte
(depicted in red) forms a ternary complex with the
chaperone-subunit complex at the P5 pocket (indicated by a
thicker line). DSE then proceeds and terminates by dissociation
of the chaperone-subunit complex and insertion of the P^*
residue in the P^* pocket.
(B) Schematic representation of
a single incorporation cycle at the usher (see text). Chaperone
and usher are colored gray and light blue, respectively. For
clarity, subunits are differentiated by color (yellow, red,
green, orange, and blue), with the last incorporated subunit in
orange and the incoming subunit in blue. The N-terminal and
C-terminal domains of the usher are indicated.
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The above figures are
reprinted
by permission from Cell Press:
Mol Cell
(2006,
22,
831-842)
copyright 2006.
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