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PDBsum entry 1pp0
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References listed in PDB file
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Key reference
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Title
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Crystal structures and electron micrographs of fungal volvatoxin a2.
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Authors
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S.C.Lin,
Y.C.Lo,
J.Y.Lin,
Y.C.Liaw.
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Ref.
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J Mol Biol, 2004,
343,
477-491.
[DOI no: ]
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PubMed id
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Abstract
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Membrane adhesion and insertion of protein are essential to all organisms, but
the underlying mechanisms remain largely unknown. Membrane pore-forming toxins
(PFTs) are potential model systems for studying these mechanisms. We have
determined the crystal structures of volvatoxin A2 (VVA2), a fungal PFT from
Volvariella volvacea, using Br-multiple-wavelength anomalous diffraction (MAD).
The VVA2 structures obtained at pH 4.6, pH 5.5 and pH 6.5 were refined to
resolutions of 1.42 A, 2.6 A and 3.2 A, respectively. The structures reveal that
the VVA2 monomer contains a single alpha/beta domain. Most of the VVA2 surface
is occupied by its oligomerization motif and two putative heparin-binding
motifs. Residues Ala91 to Ala101 display several conformations at different pH
values, which might be under the control of His87. We also found that the shape
of one putative heparin-binding motif in VVA2 appears similar to those found in
fibroblast growth factors, and the other one displays a linear polypeptide. Our
results suggest several possible intermediates of protein assembly in solution
and protein adhering to cell membranes before conformational changes. The
electron micrographs of VVA2 molecules in solution, at a protein concentration
of 1 microg ml(-1), show that they can assemble into filament-like or braid-like
oligomers in a pH-dependent way. In addition, the arc-shaped VVA2 structure
obtained at pH 6.5 suggests that VVA2 could form a two-layered helical oligomer
with 18 subunits per turn. The structures presented here could be used to
elucidate the pore-formation mechanisms of VVA2 and its structural neighbors,
Cyt toxins from Bacillus thuringiensis.
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Figure 8.
Figure 8. A helical oligomer model of VVA2 assembly. (a)
Molecular organization in VVA2 strip crystals. Five subunits in
one asymmetric unit of strip crystals are labeled. The
intermolecular interfaces between layer AB and layer CD are
marked by the name of secondary elements. (b) The electrostatic
potential surface of the opaque pentamer in (c). Anion-binding
sites are indicated. (c) Stereo view of an extended arc-shaped
oligomer generated by the molecular packing in (a). The opaque
pentamer is rotated 90° around the horizontal axis relative
to (a). The transparent pentamer indicates the generated model
after superimposition. (d) Stereo view of a unique two-layered
helical oligomer model. Subunits are colored as in (a). This
view of the helical model also shows the 9-fold symmetry. The
membrane-embedded regions are colored in light blue.
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Figure 9.
Figure 9. Comparison of the structures and the sequences
between VVA2 and Cyts. (a) Stereo C^a trace of the superimposed
VVA2 and Cyt2Aa1. VVA2 and Cyt2Aa1 are shown in blue and red,
respectively. The absolutely conserved residues are shown as
ball-and-sticks. (b) Alignment of sequences of VVA2 with Cyt2Aa1
and Cyt1Aa1 from B. thuringiensis. The alignment is according to
structural superimposition, as well as sequence identities.
Secondary structural elements of VVA2 and Cyt2Aa1 are shown in
pink and green, respectively, and 3[10]-helices are indicated.
Conservative residues are masked in crimson (absolutely
conserved) or yellow. The red residues indicate low-toxicity
mutations in Cyt1Aa1.18 The sequences of Cyt toxins after
proteolytic activation are shown.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2004,
343,
477-491)
copyright 2004.
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