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PDBsum entry 2ccl
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Cell adhesion
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PDB id
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2ccl
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References listed in PDB file
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Key reference
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Title
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Evidence for a dual binding mode of dockerin modules to cohesins.
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Authors
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A.L.Carvalho,
F.M.Dias,
T.Nagy,
J.A.Prates,
M.R.Proctor,
N.Smith,
E.A.Bayer,
G.J.Davies,
L.M.Ferreira,
M.J.Romão,
C.M.Fontes,
H.J.Gilbert.
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Ref.
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Proc Natl Acad Sci U S A, 2007,
104,
3089-3094.
[DOI no: ]
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PubMed id
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Abstract
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The assembly of proteins that display complementary activities into
macromolecular complexes is critical to cellular function. One such enzyme
complex, of environmental significance, is the plant cell wall degrading
apparatus of anaerobic bacteria, termed the cellulosome. The complex assembles
through the interaction of enzyme-derived "type I dockerin" modules
with the multiple "cohesin" modules of the scaffolding protein.
Clostridium thermocellum type I dockerin modules contain a duplicated 22-residue
sequence that comprises helix-1 and helix-3, respectively. The crystal structure
of a C. thermocellum type I cohesin-dockerin complex showed that cohesin
recognition was predominantly through helix-3 of the dockerin. The sequence
duplication is reflected in near-perfect 2-fold structural symmetry, suggesting
that both repeats could interact with cohesins by a common mechanism in
wild-type (WT) proteins. Here, a helix-3 disrupted mutant dockerin is used to
visualize the reverse binding in which the dockerin mutant is indeed rotated 180
degrees relative to the WT dockerin such that helix-1 now dominates recognition
of its protein partner. The dual binding mode is predicted to impart significant
plasticity into the orientation of the catalytic subunits within this
supramolecular assembly, which reflects the challenges presented by the
degradation of a heterogeneous, recalcitrant, insoluble substrate by a tethered
macromolecular complex.
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Figure 1.
Fig. 1. The cellulosome. (a) Schematic of the cellulosome.
The type I dockerins, appended to the catalytic subunits,
interact with the cohesin modules on the scaffoldin (CipA)
leading to the formation of the supramolecular cellulosome
complex. The type II dockerin on CipA, by binding to a type II
cohesin on the bacterial membrane, tethers the cellulosome to
the surface of C. thermocellum. (b) Internal symmetry of the WT
dockerin in complex with cohesin. Not only do residues 1–22
overlap with 35–56, but the reverse is also true, because the
dockerin shows internal 2-fold symmetry (panel b adapted from
ref. 18).
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Figure 3.
Fig. 3. The Coh-Doc interface of the native (in orange) and
S45A-T46A mutant (in blue) type I complexes. (a) Stick
representation of the hydrophobic residues on the surface of the
cohesin modules (in ribbon representation). The dockerin modules
are represented by their molecular surfaces. (b) Stick
representation of the hydrophobic residues on the surface of the
dockerin modules (in ribbon representation). The cohesin modules
are represented by their molecular surfaces. (c) Stick
representation of the hydrogen-bond network in the interface of
the Coh-DocS45A-T46A complex (in ribbon representation). Carbon
atoms are shown in yellow, oxygens are shown in red, and
nitrogens are shown in blue. All pictures were produced with the
CCP4 mg program (42).
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