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PDBsum entry 2sli
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References listed in PDB file
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Key reference
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Title
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The 1.8 a structures of leech intramolecular trans-Sialidase complexes: evidence of its enzymatic mechanism.
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Authors
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Y.Luo,
S.C.Li,
Y.T.Li,
M.Luo.
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Ref.
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J Mol Biol, 1999,
285,
323-332.
[DOI no: ]
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PubMed id
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Abstract
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Intramolecular trans-sialidase from leech (Macrobdella decora) is the first
member of the sialidase superfamily found to exhibit strict specificity towards
the cleavage of terminal Neu5Acalpha2-->3Gal linkage in sialoglycoconjugates.
Its release of 2,7-anhydro-Neu5Ac instead of Neu5Ac indicates that it catalyzes
an intramolecular trans-sialosyl reaction. Crystal structures of its complexes
with an inactive substrate analogue 2-propenyl-Neu5Ac, and with the product
2,7-anhydro-Neu5Ac, have been determined to 1.8 A resolution. The boat
conformation of the pyranose observed in the complexes supports the proposed
enzymatic mechanism that O7 of an axial 6-glycerol group attacks the positively
charged C2 of the intermediate. A generalized mechanism is proposed for the
sialidase superfamily.
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Figure 4.
Figure 4. F[o] - F[c] maps contoured at 2.0 s for the leech
IT-sialidase complexes with (a) inactive substrate analogue
2-propenyl-Neu5Ac (the terminal carbon in the 2-propenyl is not
shown). There is no density for the two terminal carbon groups
in 2-propenyl. In addition, 6-glycerol appears disordered with a
bulk density. (b) Product 2,7-anhydro-Neu5Ac; (c) also product
2,7-anhydro-Neu5Ac, soaked with substrate 3'-sialyllactose.
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Figure 6.
Figure 6. Alternate enzymatic pathways by hydrolytic
sialidases/neuraminidases, trans-sialidases, and IT-sialidases.
The favored substrate conformation (left) in the active site is
always a boat conformation. The differences between each
enzymatic mechanism are the nucleophilic attacking atoms. These
are activated water molecule in sialidase, the 3-hydroxyl of the
galactose intrans-sialidase, and the 7-hydroxyl of the substrate
sialic acid in IT-sialidase. The proximity of the hydroxyl
groups is enforced by the conformation restraints imposed by the
active site.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(1999,
285,
323-332)
copyright 1999.
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