title: Histidine-44 of the A subunit of Escherichia coli enterotoxin is involved in its enzymatic and biological activities.
abstract: 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.
authors.affiliation: Department of Microbiology, Fujita Health University School of Medicine, Aichi, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kato
authors.forename: S
authors.initials: S
authors.lastname: Imamura
authors.forename: H
authors.initials: H
authors.lastname: Kawase
authors.forename: A
authors.initials: A
authors.lastname: Miyama
authors.forename: T
authors.initials: T
authors.lastname: Tsuji
mesh_terms: D020727:ADP-Ribosylation Factors; D000376:Agmatine / Q000378:metabolism; D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D004768:Enterotoxins / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins; D019204:GTP-Binding Proteins; D006639:Histidine / Q000502:physiology*; D008956:Models, Chemical; D009244:NAD+ Nucleosidase / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011817:Rabbits; D014357:Trypsin / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D006639:Histidine; D000376:Agmatine; C027538:heat-labile enterotoxin, E coli; D011065:Poly(ADP-ribose) Polymerases; D009244:NAD+ Nucleosidase; D014357:Trypsin; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors