title: Activity of the mitogenic Pasteurella multocida toxin requires an essential C-terminal residue.
abstract: Pasteurella multocida toxin (PMT) is a potent mitogen that also affects bone resorption. PMT acts intracellularly and is therefore postulated to have several domains involved in different aspects of its function. The toxin contains eight cysteine residues. Mutants with individual substitutions for each of these residues were constructed, and the effects of these on the biological activity of the toxin were determined by cultured-cell assays. Only the most C-terminal of the eight cysteines (C1165) was essential for full activity, although mutation of the cysteine residue at position 1159 caused a slight but reproducible loss of potency. In animal challenge experiments, mutant toxin (C1165S) was not toxic to piglets, even at doses exceeding a lethal dose of active PMT 1, 000-fold. The mutant and wild-type toxins displayed identical purification characteristics, similar susceptibility to proteolytic digestion, and circular dichroism profiles, which indicated that no gross structural changes had taken place. The function of the essential C1165 residue is not yet known, although its most likely role is an enzymatic one at or near the catalytic center of the toxin.
authors.affiliation: Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire, RG20 7NN, United Kingdom.
authors.forename: P N
authors.initials: PN
authors.lastname: Ward
authors.forename: A J
authors.initials: AJ
authors.lastname: Miles
authors.forename: I G
authors.initials: IG
authors.lastname: Sumner
authors.forename: L H
authors.initials: LH
authors.lastname: Thomas
authors.forename: A J
authors.initials: AJ
authors.lastname: Lax
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D002942:Circular Dichroism; D003545:Cysteine / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D051379:Mice; D008934:Mitogens / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D016297:Mutagenesis, Site-Directed; D016979:Pasteurella multocida; D013329:Structure-Activity Relationship; D013552:Swine; D018675:Toxicity Tests; D014513:Ureter / Q000187:drug effects; D001743:Urinary Bladder / Q000187:drug effects
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D008934:Mitogens; C062258:Pasteurella multocida toxin; D003545:Cysteine