Glutamic acid‐112 of the A subunit of heat‐labile enterotoxin from enterotoxigenic <i>Escherichia coli</i> is important for ADP‐ribosyltransferase activity

Abstract

A mutant strain of enterotoxigenic Escherichia coli (E. coli pTUH 6A) produced an abnormal heat-labile enterotoxin (LT), the A subunit of which has a single amino acid substitution at position 112 (Glu-112 to Lys-112). As already reported, this mutant LT had no ileal loop and vascular permeability activities [(1990) J. Biol. Chem. 265, 22520-22525]. In this paper we report that the mutant LT showed no CHO cell elongation activity and did not activate adenylate cyclase of target cells. Moreover, no ADP-ribosyltransferase activity was detected in the mutant LT. It is concluded that the amino acid substitution at position 112 abolished the ADP-ribosyltransferase activity of the A subunit and this leads to the loss of toxic activities of LT.