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PDBsum entry 1g6e
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Antifungal protein
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PDB id
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1g6e
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References listed in PDB file
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Key reference
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Title
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Solution structure, Backbone dynamics and chitin binding of the anti-Fungal protein from streptomyces tendae tu901.
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Authors
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R.Campos-Olivas,
I.Hörr,
C.Bormann,
G.Jung,
A.M.Gronenborn.
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Ref.
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J Mol Biol, 2001,
308,
765-782.
[DOI no: ]
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PubMed id
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Abstract
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AFP1 is a recently discovered anti-fungal, chitin-binding protein from
Streptomyces tendae Tü901. Mature AFP1 comprises 86 residues and exhibits
limited sequence similarity to the cellulose-binding domains of bacterial
cellulases and xylanases. No similarity to the Cys and Gly-rich domains of plant
chitin-binding proteins (e.g. agglutinins, lectins, hevein) is observed. AFP1 is
the first chitin-binding protein from a bacterium for which anti-fungal activity
was shown. Here, we report the three-dimensional solution structure of AFP1,
determined by nuclear magnetic resonance spectroscopy. The protein contains two
antiparallel beta-sheets (five and four beta-strands each), that pack against
each other in a parallel beta-sandwich. This type of architecture is conserved
in the functionally related family II of cellulose-binding domains, albeit with
different connectivity. A similar fold is also observed in other unrelated
proteins (spore coat protein from Myxococcus xanthus, beta-B2 and gamma-B
crystallins from Bos taurus, canavalin from Jack bean). AFP1 is therefore
classified as a new member of the betagamma-crystallin superfamily. The dynamics
of the protein was characterized by NMR using amide 15N relaxation and solvent
exchange data. We demonstrate that the protein exhibits an axially symmetric
(oblate-like) rotational diffusion tensor whose principal axis coincides to
within 15 degrees with that of the inertial tensor. After completion of the
present structure of AFP1, an identical fold was reported for a Streptomyces
killer toxin-like protein. Based on sequence comparisons and clustering of
conserved residues on the protein surface for different cellulose and
chitin-binding proteins, we postulate a putative sugar-binding site for AFP1.
The inability of the protein to bind short chitin fragments suggests that
certain particular architectural features of the solid chitin surface are
crucial for the interaction.
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Figure 5.
Figure 5. Surface representation of AFP1, mapping the
electrostatic potential. The electrostatic potential is colored
from red (negative charge) to blue (positive charge). Individual
titratable amino acids are labeled according to residue type and
number. The view in the left panel is identical with that in
Figure 4(a) and the right-hand view represents a rotation by
180° around the long axis of the molecule. The two
tryptophan residues located in the putative chitin-binding site
are indicated with arrows.
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Figure 8.
Figure 8. Putative chitin-binding site of AFP1. Aromatic
side-chains potentially interacting with the hydrophobic portion
of the substrate and polar side-chains capable of contributing
to hydrogen bonding interactions with chitin are displayed in
space filling mode. All side-chains are labeled by residue type
and number.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2001,
308,
765-782)
copyright 2001.
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