ESCHERICHIA-COLI-LT-ENTEROTOXIN SUBUNIT-A DEMONSTRATES PARTIAL TOXICITY INDEPENDENT OF THE NICKING AROUND ARG192

A study was conducted into whether or not nicking of the A subunit of Escherichia coil LT enterotoxin at position Arg192 or its neighbouring amino acids Arg192 to The195 is required for its toxicity. The toxic activity of mutants created by substitution or deletion at this positi on, which lacked ADP-ribosyltransferase activity in vitro, was not com pletely obliterated and cyclic AMP was partially induced in the target cells, showing that they still displayed enzymic activity in vivo. Mo reover, although the A subunit possesses three potential sites for cle avage by furin, furin was not involved in the partial toxicity and cyc lic 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 p rocessing the A subunit after toxin binding to the cell membrane.