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PDBsum entry 1toq
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Sugar binding protein
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PDB id
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1toq
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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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Two orthorhombic crystal structures of a galactose-Specific lectin from artocarpus hirsuta in complex with methyl-Alpha-D-Galactose.
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Authors
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K.N.Rao,
C.G.Suresh,
U.V.Katre,
S.M.Gaikwad,
M.I.Khan.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2004,
60,
1404-1412.
[DOI no: ]
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PubMed id
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Abstract
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Based on their carbohydrate specificity, the jacalin family of lectins can be
divided into two groups: galactose-specific and mannose-specific. The former are
cytoplasmic proteins, whereas the latter are localized in the storage vacuoles
of cells. It has been proposed that the post-translational modification in some
of the lectins that splits their polypeptide chains into two may be crucial for
galactose specificity. The mannose-specific members of the family are
single-chain proteins that lack the above modification. Although the
galactose-specific and the mannose-specific jacalin-type lectins differ in their
sequences, they share a common fold: the beta-prism I fold, which is
characteristic of Moraceae plant lectins. Here, two crystal structures of a
jacalin-related lectin from Artocarpus hirsuta, which is specific for galactose,
in complex with methyl-alpha-D-galactose are reported. The lectin crystallized
in two orthorhombic forms and one hexagonal form under similar conditions. The
crystals had an unusually high solvent content. The structure was solved using
the molecular-replacement method using the jacalin structure as a search model.
The two orthorhombic forms were refined using data to 2.5 and 3.0 A resolution,
respectively. The structures of the A. hirsuta lectin and jacalin are identical.
In orthorhombic form I the crystal packing provides three different
micro-environments for sugar binding in the same crystal. The observed
difference in the specificity for oligosaccharides between the A. hirsuta lectin
and jacalin could only be explained based on differences in the molecular
associations in the packing and variation of the C-terminal length of the
beta-chain. The observed insecticidal activity of A. hirsuta lectin may arise
from its similar fold to domain II of the unrelated delta-endotoxin from
Bacillus thuringiensis.
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Figure 1.
Figure 1 Schematic diagram showing the hydrogen bonds between
main-chain atoms of three  -sheets
and the organization of the three Greek-key motifs in the
subunit of A. hirsuta lectin. N1 and N2 and C1 and C2 are the N-
and C-termini of the  -chain
and -chain,
respectively. The numbering in the diagram corresponds to the
residue numbering in the crystal structure.
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Figure 4.
Figure 4 (a) The quaternary structure of A. hirsuta lectin,
showing tetramer association. (b) The view of the tetramer that
shows the tetrahedral positions of the sugar-binding sites with
respect to the centre of the tetramer.
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2004,
60,
1404-1412)
copyright 2004.
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