New ribosome-inactivating proteins from seeds and fruits of the bitter gourd Momordica charantia

Effect of conventional and novel techniques on extraction yield, chemical characterisation and biological activities of proteins from bitter gourd (Momordica charantia)

The study investigates the effect of conventional and novel extraction techniques on the protein extraction yield from bitter gourd seeds (Momordica charantia). Ultrasound assisted-extraction (UAE) treatment for 30 min at 4 °C using a 20 kHz ultrasound probe resulted in the highest extraction yield of crude proteins. After purification, 9.08 ± 0.23 g of protein with 82.69 ± 0.78% purity was obtained from 100 g of M. charantia seeds on a dry basis. Mass spectrometry identified proteins with reported antidiabetic activity. Antidiabetic assays showed significantly higher antidiabetic activity for the purified protein (81.10 ± 2.64%) compared to the crude protein (32.59 ± 2.76%). In vitro cytotoxicity analysis showed minimal cytotoxicity levels at concentrations <200 μg.mL-1. Overall, UAE was effective to obtain crude protein from M. charantia seeds and a subsequent purification step enhanced antidiabetic activity. However, further research is required to demonstrate in-vivo antidiabetic activity.

Structure and Activity of a Cytosolic Ribosome-Inactivating Protein from Rice

Ribosome-inactivating proteins (RIPs) are cytotoxic enzymes that inhibit protein translation by depurinating ribosomal RNA. Although most plant RIPs are synthesized with leader sequences that sequester them away from the host ribosomes, several RIPs from cereals lack these signal peptides and therefore probably reside in the cytosol near the plant ribosomes. More than 30 RIP genes have been identified in the rice (Oryza sativa spp. japonica) genome, many of them lacking a signal peptide. This paper focuses on a presumed cytosolic type-1 RIP from rice, referred to as OsRIP1. Using 3D modeling it is shown that OsRIP1 structurally resembles other cereal RIPs and has an active site that meets the requirements for activity. Furthermore, localization studies indicate that OsRIP1-eGFP fusion proteins reside in the nucleocytoplasmic space when expressed in epidermal cells of Nicotiana benthamiana or Arabidopsis thaliana suspension cells. Finally, OsRIP1 was recombinantly produced in Escherichia coli and was demonstrated to possess catalytic activity. Interestingly, this recombinant RIP inactivates wheat ribosomes far less efficiently than rabbit ribosomes in an in vitro system. These findings raise some interesting questions concerning the mode of action and physiological role of OsRIP1. This is the first time a RIP from rice is investigated at protein level and is shown to possess biological activity.

Ribosome-inactivating proteins (RIPs) and their important health promoting property

Ribosome-inactivating proteins (RIPs), widely present in plants, certain fungi and bacteria, can inhibit protein synthesis by removing one or more specific adenine residues from the large subunit of ribosomal RNAs (rRNAs).

Ribosome-inactivating and related proteins

Ribosome-inactivating proteins (RIPs) are toxins that act as N-glycosidases (EC 3.2.2.22). They are mainly produced by plants and classified as type 1 RIPs and type 2 RIPs. There are also RIPs and RIP related proteins that cannot be grouped into the classical type 1 and type 2 RIPs because of their different sizes, structures or functions. In addition, there is still not a uniform nomenclature or classification existing for RIPs. In this review, we give the current status of all known plant RIPs and we make a suggestion about how to unify those RIPs and RIP related proteins that cannot be classified as type 1 or type 2 RIPs.

Cytotoxicity Analysis of Active Components in Bitter Melon (Momordica charantia) Seed Extracts Using Human Embryonic Kidney and Colon Tumor Cells

Bitter melon (Momordica charantia) seed extracts (BMSE) have been used as traditional medicine for treating various ailments, although in many cases, the active component(s) are unidentified. In this study, bitter melon seeds were extracted in water, ethanol, or ethanol: water (1:1). The aqueous seed extracts (BMSE-W) exhibited marked cytotoxicity towards human embryonic kidney 293T (HEK293T) and human colon tumor 116 (HCT116) cells. The activity in BMSE-W was unaffected by heat and proteinases treatments, and eluted in the total volume of size-exclusion HPLC, suggesting the small, organic nature of the active component(s). Gas chromatographic-mass spectrometic (GC-MS) analysis of the HPLC fractions identified methoxy-phenyl oxime (MPO) as a major active component. Acetophenone oxime, a commercially available structural homolog of MPO, demonstrated cytotoxicity comparable with that of the BMSE-W. The oxime functional group was found to be critical for activity. Increased poly-(ADP-ribose)-polymerase and β-actin cleavage, and chromatin condensation observed in treated cells suggested apoptosis as a plausible cause for the cytotoxicity. This study, for the first time, identified a cytotoxic oxime in BMSE-W.

Balsamin, a novel ribosome-inactivating protein from the seeds of Balsam apple Momordica balsamina

Plant seeds, a rich source of proteins, are considered important for their application as functional ingredients in a food system. A novel ribosome-inactivating protein (RIP), balsamin was purified from the seeds of Balsam apple, Momordica balsamina. Balsamin was purified by ion exchange chromatography on CM Sepharose and gel filtration on superdex-75. It has a molecular weight of 28 kDa as shown by SDS-PAGE analysis. Balsamin inhibits protein synthesis in a rabbit reticulocyte lysate-based cell free translation assay with an IC(50) of 90.6 ng ml(-1). It has RNA N-glycosidase activity and releases a 400-base long fragment termed the Endo fragment from 28S rRNA in the same manner as does saporin-6 from Saponaria officinalis. The N-terminal sequence analysis of the first 12 amino acids of balsamin revealed that it shares 83% similarity with type I RIP α-MMC from Momordica charantia and 50% similarity with β-MMC (from Momordica charantia), bryodin I (from Bryonia dioica) and luffin a (from Luffa cylindrica). Balsamin was further characterized by mass spectrometry. CD spectroscopic studies indicate that secondary structure of balsamin contains helix (23.5%), β-strand (24.6%), turn (20%) and random coil (31.9%). Thus RIPs activity expressed in vegetables like Momordica sp. advocates its usage in diet.

Flammin and velin: new ribosome inactivating polypeptides from the mushroom Flammulina velutipes

A protein designated flammin and exhibiting a molecular mass of 30kDa, and another protein designated velin and possessing a molecular mass of 19 kDa, were isolated from the fruiting bodies of the edible mushroom Flammulina velutipes. Flammin and velin inhibited translation in a rabbit reticulocyte lysate system with an IC(50) of 1.4 and 2.5 nM, respectively. Flammin demonstrated only a small degree of resemblance in N-terminal sequence to angiosperm type 1 ribosome inactivating proteins (RIPs) such as trichosanthin, alpha-momorcharin and beta-momorcharin but no sequence similarity to other mushroom RIPs. Velin manifested limited sequence homology to the A chain of abrin, a type 2 angiosperm RIP. Neither flammin nor velin showed any ribonuclease or protease activity. Both flammin and velin were unadsorbed on DEAE-cellulose and adsorbed on Affi-gel blue gel and CM-Sepharose. They were separable in gel filtration on Superdex 75 by fast protein liquid chromatography.

Purification of castamollin, a novel antifungal protein from Chinese chestnuts

A novel antifungal protein, designated castamollin, was isolated from Chinese chestnut (Castanea mollisima) seeds with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM-Sepharose and FPLC-gel filtration on Superdex 75. Castamollin possessed a novel N-terminal sequence demonstrating little similarity to N-terminal sequences of Castanea sativa chitinase. Castamollin exhibited a molecular mass of 37kDa in gel filtration and SDS-PAGE. It inhibited the activity of human immunodeficiency virus-1 reverse transcriptase with an IC(50) of 7microM and translation in a cell-free rabbit reticulocyte lysate system with an IC(50) of 2.7microM. Castamollin displayed antifungal activity against Botrytis cinerea, Mycosphaerella arachidicola, Physalospora piricola, and Coprinus comatus but was devoid of lectin activity.

Purification and characterization of alpha- and beta-benincasins, arginine/glutamate-rich peptides with translation-inhibiting activity from wax gourd seeds

Two peptides, with a molecular mass of about 11 kDa and an N-terminal sequence abundant in arginine and glutamine residues, were isolated from wax gourd seeds. The isolation protocol included affinity chromatography on Affi-gel blue gel, ion-exchange chromatography on Mono-S and gel filtration on Superdex 75. The peptides, designated alpha- and beta-benincasins, inhibited cell-free translation in a rabbit reticulocyte lysate system with an IC(50) of 20 and 320 pM, respectively. Alpha-benincasin exhibited weak antifungal activity toward Coprinus comatus and Physalospora piricola but not toward Mycosphaerella arachidicola.

Purification and characterization of charantin, a napin-like ribosome-inactivating peptide from bitter gourd (Momordica charantia) seeds

A peptide designated charantin, with a molecular mass of 9.7 kDa, was isolated from bitter gourd seeds. The procedure comprised affinity chromatography on Affi-gel blue gel, ion-exchange chromatography on Mono S and gel filtration on Superdex 75. The N-terminal sequence of charantin exhibited marked similarity to that of the 7.8-kDa napin-like peptide previously isolated from bitter gourd seeds. Charantin inhibited cell-free translation in a rabbit reticulocyte lysate system with an IC50 of 400 nm, a potency lower than that of the previously reported small ribosome-inactivating protein gamma-momorcharin (IC50 = 55 nm) which also exhibited an abundance of arginine and glutamate/glutamine residues. Charantin reacted positively in the N-glycosidase assay, yielding a band similar to that formed by the small ribosome-inactivating proteins gamma-momorcharin and luffin S.

Isolation of a novel deoxyribonuclease with antifungal activity from Asparagus officinalis seeds

A deoxyribonuclease distinct from the previously isolated asparagus ribosome-inactivating proteins, possessing a molecular weight of 30 kDa and requiring a pH of 7.5 for optimum hydrolytic activity toward herring sperm DNA, was isolated from Asparagus officinalis seeds. The isolation procedure involved extraction with saline, (NH(4))(2)SO(4) precipitation, ion-exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion-exchange chromatography on CM-Sepharose, and FPLC gel filtration on Superdex 75. The doxyribonuclease was unadsorbed onto DEAE-cellulose and Affi-gel blue gel and adsorbed onto CM-Sepharose. It exhibited the novel N-terminal sequence, GIEVIKIREL. The deoxyribonuclease was purified to a specific activity of 1584 units/mg. It was devoid of ribonuclease, protease, and HIV-1 reverse transcriptase-inhibitory activities. However, it inhibited cell-free translation in a rabbit reticulocyte lysate system with an IC(50) of 20 microM. It exhibited antifungal activity toward Botrytis cinerea but not toward Fusarium oxysporum and Mycosphaerella arachidicola.

Purification of chrysancorin, a novel antifungal protein with mitogenic activity from garland chrysanthemum seeds

A novel antifungal protein, designated chrysancorin, was isolated from seeds of Chrysanthemum coronarium var. spatiosum with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue resin, ion exchange chromatography on SP-Sepharose and FPLC-gel filtration on Superdex 75. The N-terminus of chrysancorin displays sequence similarity to the genomic sequence of chromosome 1 from Arabidopsis thaliana BAC T19E23. Chrysancorin exhibits a molecular mass of 13.4 kDa in gel filtration and SDS-polyacrylamide gel electrophoresis. It stimulates the proliferation of mouse splenocytes and inhibits the activity of human immunodeficiency virus-1 reverse transcriptase. The protein possesses antifungal activity against Botrytis cinerea, Mycosphaerella arachidicola and Physalospora piricola, but not against Rhizoctonia solani, Fusarium oxysporum and Coprinus comatus. However, we could not detect antibacterial activity against a variety of bacteria.

Flammulin: a novel ribosome-inactivating protein from fruiting bodies of the winter mushroom Flammulina velutipes

A protein with a molecular weight of 40 kDa, capable of inhibiting cell-free translation in a rabbit reticulocyte lysate system with an IC50 of 0.25 nM, was isolated from fruiting bodies of the mushroom Flammulina velutipes. The protein, designated flammulin, was devoid of ribonuclease activity. Flammulin was unadsorbed on DEAE-cellulose at neutral pH and low ionic strength and adsorbed on CM-Sepharose and Affi-gel blue gel under similar conditions. Its N-terminal sequence demonstrates sites of similarity to those of plant ribosome-inactivating proteins (RIPs).

Isolation of lectin and albumin from Pisum sativum var. macrocarpon ser. cv. sugar snap

A mannose- and glucose-binding lectin bearing considerable sequence similarity to other legume lectins was isolated using a simple procedure, from legumes of the sugar snap Pisum sativum var. macrocarpon. The lectin was unadsorbed on Affi-gel blue gel and Q-Sepharose in 10 mM Tris-HCl buffer (pH 7.2) and adsorbed on SP-Toyopearl in 50 mM NaOAc buffer (pH 5). An albumin could also be purified at the same time. It was unadsorbed on Affi-gel Blue gel, adsorbed on Q-Sepharose and unadsorbed on SP-Toyopearl under the aforementioned chromatographic conditions. The lectin was almost identical in N-terminal sequences of its alpha- and beta-subunit to lectin from P. sativum L. var. Feltham First except for the 19th N-terminal residue of the beta-subunit. The lectin was devoid of antifungal activity. Out of the 15 N-terminal amino acids examined in pea albumin, three were different between the two varieties of P. sativum.

Heterogeneity of the ribosome-inactivating protein trichosanthin in Trichosanthes kirilowii tubers

The ribosome-inactivating protein trichosanthin isolated from the tubers of Trichosanthes kirilowii, the Chinese drug Tianhuafen, has a molecular mass of approximately 26 kDa. We show here that T. kirilowii tubers also contain ribosome-inactivating proteins with a small extent of structural variation from and a larger molecular mass than trichosanthin.