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PDBsum entry 2b59
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Hydrolase/structural protein
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PDB id
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2b59
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References listed in PDB file
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Key reference
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Title
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Mechanism of bacterial cell-Surface attachment revealed by the structure of cellulosomal type ii cohesin-Dockerin complex.
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Authors
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J.J.Adams,
G.Pal,
Z.Jia,
S.P.Smith.
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Ref.
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Proc Natl Acad Sci U S A, 2006,
103,
305-310.
[DOI no: ]
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PubMed id
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Abstract
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Bacterial cell-surface attachment of macromolecular complexes maintains the
microorganism in close proximity to extracellular substrates and allows for
optimal uptake of hydrolytic byproducts. The cellulosome is a large multienzyme
complex used by many anaerobic bacteria for the efficient degradation of plant
cell-wall polysaccharides. The mechanism of cellulosome retention to the
bacterial cell surface involves a calcium-mediated protein-protein interaction
between the dockerin (Doc) module from the cellulosomal scaffold and a cohesin
(Coh) module of cell-surface proteins located within the proteoglycan layer.
Here, we report the structure of an ultra-high-affinity (K(a) = 1.44 x 10(10)
M(-1)) complex between type II Doc, together with its neighboring X module from
the cellulosome scaffold of Clostridium thermocellum, and a type II Coh module
associated with the bacterial cell surface. Identification of X module-Doc and X
module-Coh contacts reveal roles for the X module in Doc stability and enhanced
Coh recognition. This extremely tight interaction involves one face of the Coh
and both helices of the Doc and comprises significant hydrophobic character and
a complementary extensive hydrogen-bond network. This structure represents a
unique mechanism for cell-surface attachment in anaerobic bacteria and provides
a rationale for discriminating between type I and type II Coh modules.
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Figure 3.
Fig. 3. Type II Coh-XDoc complex interface contacts. (a)
Ribbon representation of type II Coh, displaying hydrophobic
interface residues as stick models on the molecular-surface
representation of XDoc. (b) Ribbon representation of XDoc,
displaying hydrophobic interface residues as stick models on the
molecular-surface representation of type II Coh. (c) Interface
hydrogen-bond network, with water molecules shown as red X and
hydrogen-bond contacts as yellow dashed lines. Type II Coh, Doc,
and X module are colored blue, green, and magenta, respectively.
Residues depicted as stick models are labeled accordingly.
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Figure 4.
Fig. 4. Interaction surfaces of type I- and type II Coh-Doc
complexes. Ribbon representations of type II Doc (green) (a) on
the molecular surface of the type II Coh (blue) and type I Doc
(red) (e) on the molecular surface of type I Coh (yellow) (21).
Representations in b and f have been rotated clockwise 90°
around the x axis, followed by a 180° clockwise rotation
around the z axis. Electrostatic surface potential
representations of C. thermocellum type II Coh (c), C.
thermocellum type II Doc (d), C. thermocellum type I Coh (21)
(g), and C. thermocellum type I Doc (21) (h). Positive regions
are shown in blue and negative regions in red. Residues
contributing to the hydrophobic surface character of C.
thermocellum type II Coh are labeled accordingly. The location
of Ile-118 on the surface of the type II Doc and the analogous
residue in the type I Doc (Lys-18) are identified. The
electrostatic surface potentials were calculated in GRASP (47)
and are contoured from -14 (red) to +14 (blue). Ca^2+ ions are
shown as orange spheres.
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