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Journal of Bacteriology, April 2000, p. 2096-2103, Vol. 182, No. 8
Department of Microbiology, Faculty of
Pharmaceutical Sciences, Tokushima Bunri University, Tokushima
770-8514, Japan
Received 4 October 1999/Accepted 20 January 2000
The iotaa component (ia) of
Clostridium perfringens ADP ribosylates nonmuscle
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Characterization of the Enzymatic Component
of Clostridium perfringens Iota-Toxin
/
actin and skeletal muscle
-actin. Replacement of Arg-295 in
ia with alanine led to a complete loss of
NAD+-glycohydrolase (NADase) and ADP-ribosyltransferase
(ARTase); that of the residue with lysine caused a drastic
reduction in NADase and ARTase activities (<0.1% of the
wild-type activities) but did not completely diminish them.
Substitution of alanine for Glu-378 and Glu-380 caused a complete loss
of NADase and ARTase. However, exchange of Glu-378 to aspartic
acid or glutamine resulted in little effect on NADase activity but
a drastic reduction in ARTase activity (<0.1% of the wild-type
activity). Exchange of Glu-380 to aspartic acid caused a drastic
reduction in NADase and ARTase activities (<0.1% of the
wild-type activities) but did not completely diminish them; that of the
residue to glutamine caused a complete loss of ARTase activity.
Replacement of Ser-338 with alanine resulted in 0.7 to 2.3% wild-type
activities, and that of Ser-340 and Thr-339 caused a reduction in these
activities of 5 to 30% wild-type activities. The kinetic analysis
showed that Arg-295 and Ser-338 also play an important role in the
binding of NAD+ to ia, that Arg-295, Glu-380,
and Ser-338 play a crucial role in the catalytic rate of NADase
activity, and that these three amino acid residues and Glu-378 are
essential for ARTase activity. The effect of amino acid replacement
in ia on ARTase activity was similar to that on lethal
and cytotoxic activities, suggesting that lethal and cytotoxic
activities in ia are dependent on ARTase activity.
*
Corresponding author. Mailing address: Department of
Microbiology, Faculty of Pharmaceutical Sciences, Tokushima Bunri
University, Yamashiro-cho, Tokushima 770-8514, Japan. Phone: 81 088-622-9611. Fax: 81 088-655-3051. E-mail:
sakurai{at}ph.bunri-u.ac.jp.
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