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Infection and Immunity, August 1999, p. 3727-3732, Vol. 67, No. 8
Project Research for Molecular
Bacteriology1 and Department of
Molecular Microbiology,2 Research Institute
for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
Received 12 January 1999/Returned for modification 19 February
1999/Accepted 5 May 1999
Bordetella dermonecrotizing toxin (DNT) stimulates the
assembly of actin stress fibers and focal adhesions by deamidating Gln63 of the small GTPase Rho. To clarify the functional and structural organization of DNT, we cloned and sequenced the DNT gene and examined
the functions of various DNT mutants. Our analyses of the nucleotide
and amino acid sequences revealed that the start codon of the DNT gene
is a GTG triplet located 39 bp upstream of the reported putative
initiation ATG codon; consequently, DNT contains an additional 13 amino
acids at its N-terminal end. All of the N-terminally truncated mutants
were found to modify Rho. The shortest fragment of DNT possessing the
Rho modification activity consists of amino acids from Ile1176 to the
C-terminal end. This fragment overlaps the region homologous to
Escherichia coli cytotoxic necrotizing factors (CNFs),
which show activity similar to that of DNT. The introduction of a
mutation at Cys1305 located in the highly conserved region between CNFs
and DNT eliminated the activity, indicating that this domain is the
catalytic center of DNT. The N-terminal fragment (1 to 531) of DNT
failed to modify Rho but reduced the DNT-induced polynucleation in
MC3T3-E1 cells when simultaneously added with the holotoxin, suggesting
competitive inhibition in the receptor-binding or internalizing step.
Our finding that DNT consists of an N-terminal receptor-binding and/or internalizing domain and a C-terminal catalytically active domain may
facilitate analysis of the overall action of the toxin on the mammalian
target cells.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Identification of Functional Domains of
Bordetella Dermonecrotizing Toxin

*
Corresponding author. Mailing address: Project Research
for Molecular Bacteriology, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan. Phone: 81-6-6879-8285. Fax:
81-6-6879-8283. E-mail: horiguti{at}biken.osaka-u.ac.jp.
Present address: Instituto de Medicina Tropical, Universidad
Nacional Mayor de San Marcos, Lima 1, Peru.
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