(1/13) Pulchellin, a highly toxic type 2 ribosome-inactivating protein from Abrus pulchellus. Cloning heterologous expression of A-chain and structural studies.

Pulchellin is a type 2 ribosome-inactivating protein isolated from seeds of the Abrus pulchellus tenuiflorus plant. This study aims to obtain active and homogeneous protein for structural and biological studies that will clarify the functional aspects of this toxin. The DNA fragment encoding pulchellin A-chain was cloned and inserted into pGEX-5X to express the recombinant pulchellin A-chain (rPAC) as a fusion protein in Escherichia coli. The deduced amino acid sequence analyses of the rPAC presented a high sequential identity (> 86%) with the A-chain of abrin-c. The ability of the rPAC to depurinate rRNA in yeast ribosome was also demonstrated in vitro. In order to validate the toxic activity we promoted the in vitro association of the rPAC with the recombinant pulchellin binding chain (rPBC). Both chains were incubated in the presence of a reduced/oxidized system, yielding an active heterodimer (rPAB). The rPAB showed an apparent molecular mass of approximately 60 kDa, similar to the native pulchellin. The toxic activities of the rPAB and native pulchellin were compared by intraperitoneal injection of different dilutions into mice. The rPAB was able to kill 50% of the tested mice with doses of 45 microg x kg(-1). Our results indicated that the heterodimer showed toxic activity and a conformational pattern similar to pulchellin. In addition, rPAC produced in this heterologous system might be useful for the preparation of immunoconjugates with potential as a therapeutic agent.  (+info)

(2/13) Structure-function analysis and insights into the reduced toxicity of Abrus precatorius agglutinin I in relation to abrin.

Abrin and agglutinin-I from the seeds of Abrus precatorius are type II ribosome-inactivating proteins that inhibit protein synthesis in eukaryotic cells. The two toxins share a high degree of sequence similarity; however, agglutinin-I is weaker in its activity. We compared the kinetics of protein synthesis inhibition by abrin and agglutinin-I in two different cell lines and found that approximately 200-2000-fold higher concentration of agglutinin-I is needed for the same degree of inhibition. Like abrin, agglutinin-I also induced apoptosis in the cells by triggering the intrinsic mitochondrial pathway, although at higher concentrations as compared with abrin. The reason for the decreased toxicity of agglutinin-I became apparent on the analysis of the crystal structure of agglutinin-I obtained by us in comparison with that of the reported structure of abrin. The overall protein folding of agglutinin-I is similar to that of abrin-a with a single disulfide bond holding the toxic A subunit and the lectin-like B-subunit together, constituting a heterodimer. However, there are significant differences in the secondary structural elements, mostly in the A chain. The substitution of Asn-200 in abrin-a with Pro-199 in agglutinin-I seems to be a major cause for the decreased toxicity of agglutinin-I. This perhaps is not a consequence of any kink formation by a proline residue in the helical segment, as reported by others earlier, but due to fewer interactions that proline can possibly have with the bound substrate.  (+info)

(3/13) Quantification of L-abrine in human and rat urine: a biomarker for the toxin abrin.

Abrin is a toxic protein found in the jequirity seed. L-Abrine (N-methyl-tryptophan) is also found in the jequirity seed and can be used as a biomarker for abrin exposure. Analysis of L-abrine was added to an existing method for quantifying ricinine as a marker for ricin exposure in human urine and analytically validated. Accuracy and reproducibility were enhanced by including a newly synthesized (13)C(1)(2)H(3)-L-abrine internal standard. One-milliliter urine samples were processed using solid-phase extraction prior to a 6-min high-performance liquid chromatography separation. Protonated molecular ions were formed via electrospray ionization in a triple-quadrupole mass spectrometer and quantified via multiple reaction monitoring. Method validation included the characterization of two enriched urine pools, which were used as quality control materials. Endogenous levels of L-abrine were quantified in a reference range of 113 random urine samples at 0.72 +/- 0.51 ng/mL. Urinary concentrations of L-abrine were monitored in an intentional rat exposure study for up to 48 h. Comparing the results from the human reference range and the animal exposure study indicates that this method is suitable for quantifying L-abrine within 24 h post-exposure. Quantification of L-abrine beyond 24 h is limited by rapid excretion of the biomarker and the level of the L-abrine dose.  (+info)

(4/13) A biophysical elucidation for less toxicity of agglutinin than abrin-a from the seeds of Abrus precatorius in consequence of crystal structure.

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(5/13) Attempted suicide, by mail order: Abrus precatorius.

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(6/13) A recombinant mutant abrin A chain expressed in Escherichia coli can be used as an effective vaccine candidate.

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(7/13) The role of the C-terminal region of pulchellin A-chain in the interaction with membrane model systems.

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(8/13) A new triterpenoid saponin from Abrus precatorius Linn.

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