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PDBsum entry 1hg7
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Antifreeze protein
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PDB id
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1hg7
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Understanding the mechanism of ice binding by type III antifreeze proteins.
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Authors
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A.A.Antson,
D.J.Smith,
D.I.Roper,
S.Lewis,
L.S.Caves,
C.S.Verma,
S.L.Buckley,
P.J.Lillford,
R.E.Hubbard.
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Ref.
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J Mol Biol, 2001,
305,
875-889.
[DOI no: ]
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PubMed id
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Abstract
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Type III antifreeze proteins (AFPs) are present in the body fluids of some polar
fishes where they inhibit ice growth at subzero temperatures. Previous studies
of the structure of type III AFP by NMR and X-ray identified a remarkably flat
surface on the protein containing amino acids that were demonstrated to be
important for interaction with ice by mutational studies. It was proposed that
0) plane of ice with the key
amino acids interacting directly with the water molecules in the ice crystal.
Here, we show that the mechanism of type III AFP interaction with ice crystals
is more complex than that proposed previously. We report a high-resolution X-ray
structure of type III AFP refined at 1.15 A resolution with individual
anisotropic temperature factors. We report the results of ice-etching
experiments that show a broad surface coverage, suggesting that type III AFP
binds to a set of planes that are parallel with or inclined at a small angle to
the crystallographic c-axis of the ice crystal. Our modelling studies, performed
with the refined structure, confirm that type III AFP can make energetically
favourable interactions with several ice surfaces.
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Figure 3.
Figure 3. Stereo figures of two regions of the ice-binding
surface showing known X-ray structures of type III AFP. (a) The
region around Gln9 and Thr18. (b) The region around Asn14 and
Gln44. The X-ray structure of the HPLC12 type III ocean pout
AFP, determined in the present study (shown in blue), is
overlapped with the previously determined structure (shown in
red; [Jia et al 1996]) and with the structure of the HPLC3
isoform [Yang et al 1998].
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Figure 4.
Figure 4. Results of the ice-etching experiment. Left,
Photograph of etched ice hemisphere grown in the presence of
HPLC-12 type III AFP from ocean pout. Right, A representation of
the etched pattern. The etched surfaces, where the antifreeze
protein bound to the ice crystal, are shaded. The unshaded
regions represent ice surfaces that have remained mirror-like
and do not have bound protein molecules. The positions of the
crystallographic a-axis and c-axis are shown in the centre of
the Figure.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2001,
305,
875-889)
copyright 2001.
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