Identification of the RNA N-glycosidase activity of ricin in castor bean extracts by an electrochemiluminescence-based assay

Structural basis of noncanonical polyphenol oxidase activity in DLL-II: A lectin from Dolichos lablab

Lectins known to possess an additional enzymatic function are called leczymes. Previous studies reported a unique polyphenol oxidase (PPO) activity in DLL-II-a leczyme from Dolichos lablab. DLL-II shares a high sequence and structural homology with DBL-another leczyme from Dolichos biflorus. Incidentally, DBL possesses lipoxygenase activity, but not the PPO activity. Legume lectins usually possess two metal-binding sites A and B. Although these sites are conserved in both DBL and DLL-II, site A in DLL-II is occupied by Mn²⁺ and site B by Ca²⁺ . In contrast, DLL-II binds Cu²⁺ and Ca²⁺ at sites A and B, respectively. Here, investigating the structural basis of PPO activity in DLL-II, we find that the PPO activity is only dependent on Cu²⁺ , but not Ca²⁺ ; and the lectin activity requires only Ca²⁺ . Further, our analysis suggests that an alternative mechanism of PPO reaction may be operative in DLL-II, which involves a mononuclear Cu²⁺ metal center; this is in contrast to the bi-nuclear Cu²⁺ metal center commonly observed in all PPOs. Importantly, structural and computational approaches employed here, we hypothesize possible PPO binding sites and the corresponding migration channels for accessing the active site.

Quantification of ricin, RCA and comparison of enzymatic activity in 18 Ricinus communis cultivars by isotope dilution mass spectrometry

The seeds of the Ricinus communis (Castor bean) plant are the source of the economically important commodity castor oil. Castor seeds also contain the proteins ricin and R. communis agglutinin (RCA), two toxic lectins that are hazardous to human health. Radial immunodiffusion (RID) and the enzyme linked immunosorbent assay (ELISA) are two antibody-based methods commonly used to quantify ricin and RCA; however, antibodies currently used in these methods cannot distinguish between ricin and RCA due to the high sequence homology of the respective proteins. In this study, a technique combining antibody-based affinity capture with liquid chromatography and multiple reaction monitoring (MRM) mass spectrometry (MS) was used to quantify the amounts of ricin and RCA independently in extracts prepared from the seeds of eighteen representative cultivars of R. communis which were propagated under identical conditions. Additionally, liquid chromatography and MRM-MS was used to determine rRNA N-glycosidase activity for each cultivar and the overall activity in these cultivars was compared to a purified ricin standard. Of the cultivars studied, the average ricin content was 9.3 mg/g seed, the average RCA content was 9.9 mg/g seed, and the enzymatic activity agreed with the activity of a purified ricin reference within 35% relative activity.

A peptide with potent antifungal and antiproliferative activities from Nepalese large red beans

An antifungal defensin-like peptide with a molecular mass of 7.1kDa was isolated from dried Nepalese large red beans (Phaseolus angularis). The purification protocol employed included ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on SP-Sepharose, and gel filtration by fast protein liquid chromatography on Superdex 75. The antifungal peptide was unadsorbed on DEAE-cellulose, and adsorbed on Affi-gel blue gel and SP-Sepharose. The antifungal peptide inhibited mycelial growth in Fusarium oxysporum and Mycosphaerella arachidicola with an IC(50) value of 1.4 and 1.8 microM, respectively. It did not inhibit HIV-1 reverse transcriptase when tested up to 200 microM. It exerted an antiproliferative action on L1210 leukemia cells and MBL2 lymphoma cells with an IC(50) of 15 and 60 microM, respectively.

Application of deadenylase electrochemiluminescence assay for ricin to foods in a plate format

A recently developed bead-based deadenylase electrochemiluminescence assay for ricin is simple and sensitive in its ability to detect ricin, based on the catalytic activity of the toxin subunit, ricin A chain. The assay was modified to work in a 96-well plate format and evaluated by using juice samples. The plate-based assay, unlike the bead-based assay, includes wash steps that enable the removal of food particles. These steps minimize matrix effects and improve the signal-to-noise ratios and limits of detection (LOD). The LOD values for ricin in apple juice, vegetable juice, and citrate buffer by using the bead-based assay were 0.4, 1, and 0.1 microg/ml, respectively. In contrast, the LOD values for ricin by using the plate-based assay were 0.04, 0.1, and 0.04 microg/ml in apple juice, vegetable juice, and citrate buffer, respectively. The plate-based assay displayed three- to 10-fold lower LOD values than did the bead-based assay. Signal-to-noise ratios for the plate-based assay were comparable to those for the bead-based assay for ricin in citrate buffer, but 2- to 4.5-fold higher when the plate-based assay was used for analysis of juice samples.