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PDBsum entry 1hoz
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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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Structure and function of a novel purine specific nucleoside hydrolase from trypanosoma vivax.
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Authors
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W.Versées,
K.Decanniere,
R.Pellé,
J.Depoorter,
E.Brosens,
D.W.Parkin,
J.Steyaert.
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Ref.
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J Mol Biol, 2001,
307,
1363-1379.
[DOI no: ]
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PubMed id
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Abstract
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The purine salvage pathway of parasitic protozoa is currently considered as a
target for drug development because these organisms cannot synthesize purines de
novo. Insight into the structure and mechanism of the involved enzymes can aid
in the development of potent inhibitors, leading to new curative drugs.
Nucleoside hydrolases are key enzymes in the purine salvage pathway of
Trypanosomatidae, and they are especially attractive because they have no
equivalent in mammalian cells. We cloned, expressed and purified a nucleoside
hydrolase from Trypanosoma vivax. The substrate activity profile establishes the
enzyme to be a member of the inosine-adenosine-guanosine-preferring nucleoside
hydrolases (IAG-NH). We solved the crystal structure of the enzyme at 1.6 A
resolution using MAD techniques. The complex of the enzyme with the substrate
analogue 3-deaza-adenosine is presented. These are the first structures of an
IAG-NH reported in the literature. The T. vivax IAG-NH is a homodimer, with each
subunit consisting of ten beta-strands, 12 alpha-helices and three small
3(10)-helices. Six of the eight strands of the central beta-sheet form a motif
resembling the Rossmann fold. Superposition of the active sites of this IAG-NH
and the inosine-uridine-preferring nucleoside hydrolase (IU-NH) of Crithidia
fasciculata shows the molecular basis of the different substrate specificity
distinguishing these two classes of nucleoside hydrolases. An "aromatic
stacking network" in the active site of the IAG-NH, absent from the IU-NH,
imposes the purine specificity. Asp10 is the proposed general base in the
reaction mechanism, abstracting a proton from a nucleophilic water molecule.
Asp40 (replaced by Asn39 in the IU-NH) is positioned appropriately to act as a
general acid and to protonate the purine leaving group. The second general acid,
needed for full enzymatic activity, is probably part of a flexible loop located
in the vicinity of the active site.
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Figure 3.
Figure 3. Representative section of the electron density
map (b-strand 10; Leu304-Arg309) of uncomplexed T. vivax IAG-NH,
contoured at 1 s. (a) Experimental map at 1.6 Å resolution
after density modification with DM. (b) The 2F[o] - F[c] map
after refinement at a resolution of 1.6 Å. The Figure was
made with CONSCRIPT[69] and MOLSCRIPT. [70]
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Figure 5.
Figure 5. Two orientations of a T. vivax IAG-NH subunit.
3-Deaza-adenosine is represented as ball-and-stick model, the
calcium ion and the catalytic water molecule are depicted as
dark and light blue spheres, respectively. The substrate
analogue 3-deaza-adenosine is bound at the C terminus of the
eight-stranded central b-sheet. The amino acid residues between
His247 and Asp253 are missing from the model. The Figure was
prepared with MOLSCRIPT.[70]
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2001,
307,
1363-1379)
copyright 2001.
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