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Infect Immun, June 1998, p. 2420-2425, Vol. 66, No. 6
Graduate Group in
Biophysics1 and
Department of
Chemistry,2 University of California, and
Material Sciences Division, Lawrence Berkeley National
Laboratory,3 Berkeley, California 94720
Received 2 February 1998/Returned for modification 16 February
1998/Accepted 4 March 1998
Botulinum neurotoxin serotype A is initially released from the
bacterium Clostridium botulinum as a stable 900-kDa
complex. The serotype A 900-kDa complex is one of the forms of the
toxin being used as a therapeutic agent for the treatment
of various neuromuscular disorders. Previous experiments have
demonstrated that the 900-kDa complex form of the toxin protects the
toxin from the harsh conditions of the gastrointestinal tract. To
provide molecular level details of the stability and equilibrium of the 900-kDa complex, the nontoxic component, and the toxic
(botulinum neurotoxin) component, the three species have been
investigated with a series of biophysical techniques at the molecular
level (dynamic light scattering, proteolysis, circular dichroism, pH incubations, and agglutination assays). These experiments were conducted under harsh conditions which mimic those found along the gastrointestinal tract. Separately, exposure to denaturing and
proteolytic conditions degrades both the botulinum neurotoxin and the
nontoxic component. In the 900-kDa complex, the botulinum neurotoxin is
protected during exposure to the gastrointestinal environment and the
nontoxic component is slightly modified. Surprisingly, the toxin
protects the ability of the nontoxic component to agglutinate erythrocytes. Contrary to previous reports, the purified 900-kDa complex did not have agglutination ability until after exposure to the
proteolytic conditions. These experiments provide new evidence and
detail for the theory that the nontoxic component and the toxic
component protect one another during exposure to harsh conditions, and
a molecular model is presented for the passage of the toxin through the
gastrointestinal tract.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Biophysical Characterization of the Stability of the
150-Kilodalton Botulinum Toxin, the Nontoxic Component, and the
900-Kilodalton Botulinum Toxin Complex Species
*
Corresponding author. Mailing address: Department of
Chemistry, University of California, Berkeley, CA 94720. Phone: (510) 643-8285. Fax: (510) 643-9290. E-mail:
stevens{at}adrenaline.berkeley.edu.
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