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PDBsum entry 2j3v
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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 action of the binary c2 toxin from clostridium botulinum.
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Authors
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C.Schleberger,
H.Hochmann,
H.Barth,
K.Aktories,
G.E.Schulz.
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Ref.
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J Mol Biol, 2006,
364,
705-715.
[DOI no: ]
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PubMed id
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Abstract
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C2 toxin from Clostridium botulinum is composed of the enzyme component C2-I,
which ADP-ribosylates actin, and the binding and translocation component C2-II,
responsible for the interaction with eukaryotic cell receptors and the following
endocytosis. Three C2-I crystal structures at resolutions of up to 1.75 A are
presented together with a crystal structure of C2-II at an appreciably lower
resolution and a model of the prepore formed by fragment C2-IIa. The C2-I
structure was determined at pH 3.0 and at pH 6.1. The structural differences are
small, indicating that C2-I does not unfold, even at a pH value as low as 3.0.
The ADP-ribosyl transferase activity of C2-I was determined for alpha and
beta/gamma-actin and related to that of Iota toxin and of mutant S361R of C2-I
that introduced the arginine observed in Iota toxin. The substantial activity
differences between alpha and beta/gamma-actin cannot be explained by the
protein structures currently available. The structure of the transport component
C2-II at pH 4.3 was established by molecular replacement using a model of the
protective antigen of anthrax toxin at pH 6.0. The C-terminal receptor-binding
domain of C2-II could not be located but was present in the crystals. It may be
mobile. The relative orientation and positions of the four other domains of
C2-II do not differ much from those of the protective antigen, indicating that
no large conformational changes occur between pH 4.3 and pH 6.0. A model of the
C2-IIa prepore structure was constructed based on the corresponding assembly of
the protective antigen. It revealed a surprisingly large number of asparagine
residues lining the pore. The interaction between C2-I and C2-IIa and the
translocation of C2-I into the target cell are discussed.
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Figure 3.
Figure 3. Stereoview of C2-I (carrying NAD^+ transferred from
IotaA) and β/γ-actin (top, accession code 2BTF) in the
proposed reaction geometry. Both models are shown in an
inflated-stick-mode and opened by a total angle of 32°
towards the viewer so that the contacting surfaces can be
visualized. A dotted straight line between the C1′-carbon of
NAD^+ and the modified Arg177 of actin indicates the ADP-ribosyl
transfer. The three α versus β/γ-actin substitutions on the
interaction surface as well as Mut-S361R of C2-I are colored
pink and labeled (black).
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Figure 6.
Figure 6. Stereoview of a model of the C2-IIa heptamer as
derived from a superposition with the established prepore
structure of PA[63] from anthrax toxin.^4 (a) Model of the
C2-IIa prepore shown in an inflated-stick-mode. The expected
docking site of the enzymic component C2-I as derived from
experimental data for anthrax toxin is yellow.^19^,^20 (b)
Ribbon plot of two adjacent subunits of the C2-IIa model as
viewed from the lumen of the prepore. All residues pointing into
the prepore lumen are drawn out and numbered. The mobile loop
containing Phe428 is labeled. The blue sphere marks position
319, which was suggested to form the tip of the putative
α-hemolysin-like β-barrel inserted into the membrane.^4
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2006,
364,
705-715)
copyright 2006.
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