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PDBsum entry 1jn2
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Sugar binding protein
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PDB id
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1jn2
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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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Functional equality in the absence of structural similarity: an added dimension to molecular mimicry.
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Authors
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M.Goel,
D.Jain,
K.J.Kaur,
R.Kenoth,
B.G.Maiya,
M.J.Swamy,
D.M.Salunke.
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Ref.
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J Biol Chem, 2001,
276,
39277-39281.
[DOI no: ]
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PubMed id
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Abstract
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The crystal structure of meso-tetrasulfonatophenylporphyrin complexed with
concanavalin A (ConA) was determined at 1.9 A resolution. Comparison of this
structure with that of ConA bound to methyl alpha-d-mannopyranoside provided
direct structural evidence of molecular mimicry in the context of ligand
receptor binding. The sulfonatophenyl group of
meso-tetrasulfonatophenylporphyrin occupies the same binding site on ConA as
that of methyl alpha-d-mannopyranoside, a natural ligand. A pair of stacked
porphyrin molecules stabilizes the crystal structure by end-to-end cross-linking
with ConA resulting in a network similar to that observed upon agglutination of
cells by lectins. The porphyrin binds to ConA predominantly through hydrogen
bonds and water-mediated interactions. The sandwiched water molecules in the
complex play a cementing role, facilitating favorable binding of porphyrin.
Seven of the eight hydrogen bonds observed between methyl
alpha-d-mannopyranoside and ConA are mimicked by the sulfonatophenyl group of
porphyrin after incorporating two water molecules. Thus, the similarity in
chemical interactions was manifested in terms of functional mimicry despite the
obvious structural dissimilarity between the sugar and the porphyrin.
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Figure 2.
Fig. 2. The stereo view of the molecular conformation of
H[2]TPPS in the asymmetric unit of the crystals of the
H[2]TPPS·ConA complex. A, the F[o]  F[c] map
in the ligand-binding site on ConA, scaled at 3.2  , showing
half of the H[2]TPPS molecule corresponding to the asymmetric
unit. The porphyrin model has been built into the map (thick
black lines). The water molecules in the region have also been
shown as black spheres. The surrounding ConA residues are shown
as thin gray lines. B, a stereo view of the porphyrin
conformation as it appears in complex with ConA molecule. The
non-carbon atoms belonging to one asymmetric unit are labeled.
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Figure 3.
Fig. 3. A stereo view of the unique self-stacking
arrangement of the porphyrin molecules in the
H[2]TPPS·ConA complex. The stacked porphyrins are
slightly staggered to prevent steric clashes between the side
groups (thick blue sticks). Two stacked porphyrins are
surrounded by four independent monomers of ConA. The porphyrin
in the asymmetric unit interacts with only six amino acid
residues of ConA. The ConA residues (sticks) and water molecules
(spheres) of one asymmetric unit involved in interactions with
porphyrin are shown in the same color.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2001,
276,
39277-39281)
copyright 2001.
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