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PDBsum entry 1c1f
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Sugar binding protein
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PDB id
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1c1f
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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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High-Resolution structure of the conger eel galectin, Congerin i, In lactose-Liganded and ligand-Free forms: emergence of a new structure class by accelerated evolution.
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Authors
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T.Shirai,
C.Mitsuyama,
Y.Niwa,
Y.Matsui,
H.Hotta,
T.Yamane,
H.Kamiya,
C.Ishii,
T.Ogawa,
K.Muramoto.
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Ref.
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Structure, 1999,
7,
1223-1233.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: Congerin I is a member of the galectin (animal
beta-galactoside-binding lectin) family and is found in the skin mucus of conger
eel. The galectin family proteins perform a variety of biological activities.
Because of its histological localization and activity against marine bacteria
and starfish embryos, congerin I is thought to take part in the eels' biological
defense system against parasites. RESULTS: The crystal structure of congerin I
has been determined in both lactose-liganded and ligand-free forms to 1. 5 A and
1.6 A resolution, respectively. The protein is a homodimer of 15 kDa subunits.
Congerin I has a beta-sheet topology that is markedly different from those of
known relatives. One of the beta-strands is exchanged between two identical
subunits. This strand swap might increase the dimer stability. Of the known
galectin complexes, congerin I forms the most extensive interaction with lactose
molecules. Most of these interactions are substituted by similar interactions
with water molecules, including a pi-electron hydrogen bond, in the ligand-free
form. This observation indicates an increased affinity of congerin I for the
ligand. CONCLUSIONS: The genes for congerin I and an isoform, congerin II, are
known to have evolved under positive selection pressure. The strand swap and the
modification in the carbohydrate-binding site might enhance the cross-linking
activity, and should be the most apparent consequence of positive selection. The
protein has been adapted to functioning in skin mucus that is in direct contact
with surrounding environments by an enhancement in cross-linking activity. The
structure of congerin I demonstrates the emergence of a new structure class by
accelerated evolution under selection pressure.
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Figure 6.
Figure 6. Stereo pairs of omit maps around
carbohydrate-binding clefts of (a) the lactoseliganded form and
(b) the ligand-free form of congerin I. The lactose molecule or
the water molecules in the cleft of the ligand-free form were
excluded from phase calculation. The omitted atoms are shown in
red, and the others are shown in blue. Both electron-density
maps (green) are contoured at the 3.5s level. Glc is glucose and
Gal is galactose.
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1999,
7,
1223-1233)
copyright 1999.
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