title: Canatoxin, a toxic protein from jack beans (Canavalia ensiformis), is a variant form of urease (EC 3.5.1.5): biological effects of urease independent of its ureolytic activity.
abstract: Canatoxin is a toxic protein from Canavalia ensiformis seeds, lethal to mice (LD(50)=2 mg/kg) and insects. Further characterization of canatoxin showed that its main native form (184 kDa) is a non-covalently linked dimer of a 95 kDa polypeptide containing zinc and nickel. Partial sequencing of internal peptides indicated homology with urease (EC 3.5.1.5) from the same seed. Canatoxin has approx. 30% of urease's activity for urea, and K(m) of 2-7 mM. The proteins differ in their affinities for metal ions and were separated by affinity chromatography on a Zn(2+) matrix. Similar to canatoxin, urease activates blood platelets and interacts with glycoconjugates. In contrast with canatoxin, no lethality was seen in mice injected with urease (10 mg/kg). Pretreatment with p-hydroxymercuribenzoate irreversibly abolished the ureolytic activity of both proteins. On the other hand, p-hydroxymercuribenzoate-treated canatoxin was still lethal to mice, and both treated proteins were fully active in promoting platelet aggregation and binding to glycoconjugates. Taken together, our data indicate that canatoxin is a variant form of urease. Moreover, we show for the first time that these proteins display several biological effects that are unrelated to their enzymic activity for urea.
authors.affiliation: Department of Biophysics, IB, Universidade Federal Rio Grande do Sul, Av. Bento Gonçalves n degrees 9500, Porto Alegre, RS, CEP 91.501-970, Brazil.
authors.forename: C
authors.initials: C
authors.lastname: Follmer
authors.forename: G B
authors.initials: GB
authors.lastname: Barcellos
authors.forename: R B
authors.initials: RB
authors.lastname: Zingali
authors.forename: O L
authors.initials: OL
authors.lastname: Machado
authors.forename: E W
authors.initials: EW
authors.lastname: Alves
authors.forename: C
authors.initials: C
authors.lastname: Barja-Fidalgo
authors.forename: J A
authors.initials: JA
authors.lastname: Guimarães
authors.forename: C R
authors.initials: CR
authors.lastname: Carlini
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology; D002850:Chromatography, Gel; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D006388:Hemagglutinins / Q000378:metabolism; D006902:Hydroxymercuribenzoates / Q000494:pharmacology; D007700:Kinetics; D037102:Lectins / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D027805:Phaseolus / Q000201:enzymology*; D037121:Plant Lectins; D010940:Plant Proteins; D011485:Protein Binding; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D014118:Toxins, Biological; D014508:Urea / Q000378:metabolism; D014510:Urease / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D015032:Zinc / Q000378:metabolism
chemical_list: D006388:Hemagglutinins; D006902:Hydroxymercuribenzoates; D037102:Lectins; D037121:Plant Lectins; D010940:Plant Proteins; D014118:Toxins, Biological; C030601:4-hydroxymercuribenzoate; C032815:canatoxin; D014508:Urea; D014510:Urease; D015032:Zinc