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PDBsum entry 1f94
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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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The atomic resolution structure of bucandin, A novel toxin isolated from the malayan krait, Determined by direct methods.
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Authors
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P.Kuhn,
A.M.Deacon,
S.Comoso,
G.Rajaseger,
R.M.Kini,
I.Usón,
P.R.Kolatkar.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2000,
56,
1401-1407.
[DOI no: ]
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PubMed id
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Abstract
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Bucandin is a novel presynaptic neurotoxin isolated from Bungarus candidus
(Malayan krait). It has the unique property of enhancing presynaptic
acetylcholine release and represents a family of three-finger toxins with an
additional disulfide in the first loop. There are no existing structures from
this sub-category of three-finger toxins. The X-ray crystal structure of
bucandin has been determined by the Shake-and-Bake direct-methods procedure. The
resulting electron-density maps were of outstanding quality and allowed the
automated tracing of 61 of the 63 amino-acid residues, including their side
chains, and the placement of 48 solvent molecules. The 0.97 A resolution
full-matrix least-squares refinement converged to a crystallographic R factor of
12.4% and the final model contains 118 solvent molecules. This is the highest
resolution structure of any member of the three-finger toxin family and thus it
can serve as the best model for other members of the family. Furthermore, the
structure of this novel toxin will help in understanding its unique ability to
enhance acetylcholine release. The unique structure resulting from the fifth
disulfide bond residing in the first loop improves the understanding of other
toxins with a similar arrangement of disulfide bonds.
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Figure 2.
Figure 2 Electron-density maps obtained from (a) SnB v2.0, (b)
the final refined model (2F[o] - F[c]). The maps are contoured
at 1.0  (gray)
and 5.0 (magenta).
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Figure 5.
Figure 5 Structural comparisons of (a) bucandin with cobratoxin
(1ctx), (b) erabutoxin (3ebx) and (c) bungarotoxin (2abx).
Bucandin is colored orange in each figure. The similarity of
structures is apparent, as well as the significant differences
within the loop regions. The nearly 90° turn of the first loop
of bucandin relative to the rest of the molecule shows a
significant difference compared with other toxins. The presence
of a fourth  -strand
in bucandin is clearly seen on the left of the molecule.
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2000,
56,
1401-1407)
copyright 2000.
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