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
| Autor: | C, Follmer, G B, Barcellos, R B, Zingali, O L, Machado, E W, Alves, C, Barja-Fidalgo, J A, Guimarães, C R, Carlini |
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| Rok vydání: | 2001 |
| Předmět: |
Blood Platelets
Phaseolus Dose-Response Relationship Drug Sequence Homology Amino Acid Molecular Sequence Data Urease Molecular Weight Kinetics Mice Zinc Hemagglutinins Lectins Chromatography Gel Animals Hydroxymercuribenzoates Urea Electrophoresis Polyacrylamide Gel Amino Acid Sequence Rabbits Plant Lectins Dimerization Plant Proteins Protein Binding Toxins Biological Research Article |
| Zdroj: | The Biochemical journal. 360(Pt 1) |
| ISSN: | 0264-6021 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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