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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.

SUBMITTER: Follmer C

PROVIDER: S-EPMC1222220 | biostudies-other | 2001 Nov

REPOSITORIES: biostudies-other

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Project description:Serine proteases has been vastly reported to be found (and identified) only in seed extracts of Canavalia ensiformis (C. ensiformis), however, our group observed expressive serine protease activities in aqueous extracts from leaves, seeds, roots, and stem, especially in a leaf extract obtained with distillated water (CE-A). Additionally, this extract demonstrated very good stability in high temperatures and in the presence of chemical agents. In order to study the serine protease activity in leaves, CE-A was submitted to benzamidine-sepharose affinity column and an enriched fraction of serine proteases, named CE-ABza was purified 1.65 fold, yielding a total recovery of about 62%. Based upon zymographic analysis in a gelatin-SDS-PAGE-, the CE-ABza fraction presented an enzymatic activity band at approximately 90 kDa molecular mass region under non-reducing conditions and three bands at 17, 32 and also at 90 kDa under reducing condition. This fraction was able to hydrolyze, in a different way, peptidomimetic and protein substrates. The maximal activity was observed at basic pH values (8.0 to 9.5) and temperature about 40°C. These enzymes exhibited important thermal stability and were significantly inhibited by serine protease inhibitors, such as benzamidine and TPCK. Calcium, magnesium, manganese and zinc ions had a negative modulation on the CE-ABza activity. Mass spectrometry-based proteomics approach identified showed homology with 11 plant proteases from different legumes species, indicating their presence or demonstrating that CE-Bza proteases share specific region of the primary structure of theses enzyme, although the C. ensiformis genome and protein databases are yet to be publicly available. These results demonstrated that these molecules found in both the CE-A extract and the CE-ABza fraction presented important properties that could be used as potential pharmacological and biotechnological targets as therapeutic option. Besides, identification and characterization of C. ensiformis proteases contribute to the studies of plant enzymes.

Dataset Information

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.

Similar Datasets

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