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Microbiology 143 (1997), 1797-1804; DOI  10.1099/00221287-143-6-1797
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Escherichia coli LT enterotoxin subunit A demonstrates partial toxicity independent of the nicking around Arg192

Takao Tsuji1, Michio Kato1, Hidetsugu Kawase1, Seiji Imamura1, Hirofumi Kamiya1, Yoshio Ichinose2 and Akio Miyama1

1 Department of Microbiology, Fujita Health University, School of Medicine, Toyoake, Aichi, 470-11, Japan
2 Department of Bacteriology, Institute of Tropical Medicine, Nagasaki University, 1-12-4, Sakamoto, Nagasaki 852, Japan

Author for correspondence: Takao Tsuji. Tel: +81 562 93 2433. Fax: +81 562 93 2649. e-mail: ttsuji@fujita-hu.ac.jp

ABSTRACT

A study was conducted into whether or not nicking of the A subunit of Escherichia coli LT enterotoxin at position Arg192 or its neighbouring amino acids Arg192 to The 195 is required for its toxicity. The toxic activity of mutants created by substitution or deletion at this position, which lacked ADP-ribosyltransferase activity in vitro, was not completely obliterated and cyclic AMP was partially induced in the target cells, showing that they still displayed enzymic activity in vivo. Moreover, although the A subunit possesses three potential sites for cleavage by furin, furin was not involved in the partial toxicity and cyclic AMP induction observed. These data suggest that target cells have a nick mechanism that operates at sites other than those around Arg192 or those recognized by furin, which generates an active fragment by processing the A subunit after toxin binding to the cell membrane.

Keywords: heat-labile enterotoxin, enterotoxigenic Escherichia coli,, nicking, furin






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Copyright © 1997 Society for General Microbiology.