Open AccessHistidine‐44 of the A subunit of Escherichia coli enterotoxin is involved in its enzymatic and biological activities
Author(s) -
Kato Michio,
Imamura Seiji,
Kawase Hidetsugu,
Miyama Akio,
Tsuji Takao
Publication year - 1997
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1997.tb10431.x
Subject(s) - histidine , biochemistry , escherichia coli , enterotoxin , nad+ kinase , adp ribosylation , glutamic acid , alanine , amino acid , recombinant dna , chemistry , protein subunit , enzyme , biology , gene
We examined the role in toxicity of histidine‐44 of the A subunit of Escherichia coli enterotoxin, which is located in the active site cavity close to glutamic acid‐112. Although amino acid substitution of histidine‐44 usually renders a mutant toxin unstable to trypsin, one mutant, alanine‐44 (His44Ala) was found to be stable. His44Ala did not show any agmatine:ADP‐ribosyltransferase activity in the presence or absence of recombinant ADP‐ribosylation factor. It showed no diarrheal or rabbit skin permeability activity and was a competitor in enterotoxin‐ADP‐ribosyltransferase assays containing recombinant ADP‐ribosylation factor. These results suggest that like glutamic acid‐112, histidine‐44 plays an essential role in toxicity. A tentative model, which explains NAD + catalysis and the transfer of the ADP‐ribosyl moiety to a target amino acid, is proposed for histidine‐44 and glutamic acid‐112.