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Infect. Immun., Jun 1997, 2225-2232, Vol 65, No. 6
NM Bakry, Y Kamata and LL Simpson
The binding of iodinated botulinum toxin type B to nerve membranes was
studied by using rat and mouse preparations. The toxin was examined both in
the single-chain and in the proteolytically processed dichain form, and
binding sites both in the spinal cord and in various brain regions were
assayed. Rat and mouse brains possessed specific binding sites for
botulinum toxin type B. The average Kd values for the various rat and mouse
membrane preparations examined were 4.2 +/- 0.7 nM and 3.7 +/- 0.9 nM,
respectively. The average Bmax values for the same tissue preparations were
7.3 +/- 0.7 pmol/mg of protein and 7.5 +/- 1.9 pmol/mg protein,
respectively. The binding of botulinum toxin type B to rat brain membranes
was not antagonized by a polyclonal antibody against the cytosolic domain
of synaptotagmin 1 or by a monoclonal antibody directed against the luminal
domain of synaptotagmin 1. In addition, these antibodies did not protect
the mouse phrenic nerve- hemidiaphragm from toxin-induced neuromuscular
blockade. Extraction of whole-brain mRNA and injection into Xenopus oocytes
led to expression of binding sites for botulinum toxin. Extraction and
injection of cerebellar mRNA led to expression of a higher density of
binding sites. The number of binding sites was not diminished when oocytes
were pretreated with antibodies against the cytosolic and luminal domains
of synaptotagmin 1. These findings are likely to aid in the isolation,
characterization, and reconstitution of toxin binding sites.
Copyright © 1997, American Society for Microbiology
Expression of botulinum toxin binding sites in Xenopus oocytes
Department of Medicine, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
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