Purification and partial characterization of a mitogenic lectin from the latex of Euphorbia marginata

Review: Laticifer as a plant defense mechanism

Laticifers have been utilized as paradigms to enhance comprehension of specific facets of plant ecology and evolution. From the beginning of seedling growth, autonomous laticifer networks are formed throughout the plant structure, extending across all tissues and organs. The vast majority of identified products resulting from laticifer chemistry and metabolism are linked to plant defense. The latex, which is the fluid contained within laticifers, is maintained under pressure and has evolved to serve as a defense mechanism against both aggressors and invaders, irrespective of their capabilities or tactics. Remarkably, the latex composition varies among different species. The current goal is to understand the specific functions of various latex components in combating plant enemies. Therefore, the study of latex's chemical composition and proteome plays a critical role in advancing our understanding about plant defense mechanisms. Here, we will discuss some of these aspects.

A Comprehensive Review on Euphorbiaceae lectins: Structural and Biological Perspectives

Euphorbiaceae, also known as the spurge family, is a large group of flowering plants. Despite being tropical natives, they are now widespread. Due to its medicinal and commercial importance, this family of plants attracted a lot of attention in the scientific community. The distinctive characteristic of the family is production of milky latex, which is a rich source of several lectins, the proteins that bind carbohydrates. Although their function is unclear, they are believed to defend plants against damaging phytopathogenic microorganisms, insects, and predatory animals. Additionally, they serve as crucial metabolic regulators under a variety of stressors. Detection, separation, purification, and characterization of lectins from the Euphorbiaceae family - mostly from the latex of plants - began over 40 years ago. This effort produced over 35 original research papers that were published. However, no systematic review that compiles these published data has been presented yet. This review summarizes and describes several procedures and protocols employed for extraction and purification of lectins belonging to this family. Physicochemical properties and biological activities of the lectins, along with their medicinal and pharmacological properties, have also been analyzed. Additionally, using examples of ricin and ricin agglutinin, we have structurally analyzed characteristics of the lectin known as Ribosome Inactivating Protein Type II (RIP-Type II) that belongs to this family. We anticipate that this review article will offer a useful compendium of information on this important family of lectins, show the scientists involved in lectin research the gaps in our knowledge, and offer insights for future research.

Purification and partial characterization of a ribosome-inactivating protein from the latex of Euphorbia trigona Miller with cytotoxic activity toward human cancer cell lines

BACKGROUND

The objective of this study is to investigate the cytotoxic activity of three isolectins purified from the latex of Euphorbia trigona Miller.

HYPOTHESIS

Among lectins are the ribosome-inactivating proteins (RIPs), which are potent inhibitors of protein synthesis in cells and in cell-free systems.

RESULTS

Three isolectins, ETR1, ETR2 and ETR3, were purified by anion exchange chromatography. Both ETR1 and ETR3 yielded a single band on SDS-PAGE under reducing conditions, corresponding to a molecular weight of 32 g mol(-1), while ETR2 yielded two bands corresponding to 31 and 33 g mol(-1). When non-reducing conditions were used molecular weight decreased, indicating the presence of intrachain disulfide bonds. Size-exclusion chromatography revealed proteins of apparent molecular weight of 59-63 g mol(-1), suggesting a dimeric nature, with subunits not being held together by disulfide linkage. ETR1, ETR2 and ETR3 hemagglutinated human, sheep and rat erythrocytes and this hemagglutination was specifically inhibited by galactose and its derivatives. The lectins studied were thermostable up to 60 °C and their observed activity was maintained across pH range 5-12. These lectins, from the latex of Euphorbia trigona, are potent inhibitors of eukaryotic protein synthesis in a cell-free system. Flow cytometry analysis revealed the antiproliferative activity of them toward A549, HeLa, H116, HL-60 cell lines.

CONCLUSION

Euphorbia trigona isolectins are RIPs with cytotoxic activity toward human cancer cell lines.

New promising Euphorbiaceae extracts with activity in human lymphocytes from primary cell cultures

CONTEXT

Euphorbiaceae plants exhibit anti-inflammatory and immunomodulatory properties.

METHODS

We evaluated the activity of 14 extracts from seven Euphorbiaceae plants on primary immune cell cultures from healthy individuals. Peripheral blood mononuclear cells (PBMC) were exposed to the extracts w/o phytohaemagglutinin A or cycloheximide as agents that induce proliferation or apoptosis in PBMC, respectively.

RESULTS

We found that five up to 14 Euphorbiaceae's extracts had the ability to modulate at least one of the immune parameters evaluated in this study. However, only the latex extracts of Euphorbia cotinifolia and Euphorbia tirucalli strongly induced both proliferation and apoptosis in PBMC. These extracts were further subfractioned by silica gel column chromatography. Two subfractions with enhanced activity in comparison to the crude extracts were obtained. Although these subfractions induced proliferation on both CD3(+) and CD3(-) cells, the most prominent effects were observed in the former subpopulation. Interestingly, the subfraction from E. tirucalli induced lymphocyte proliferation without the need of accessory cells; this ability was not inhibited by the carbohydrates d-galactose and α-Methyl-D-Mannopyranoside.

CONCLUSIONS

Altogether, these results reveal the presence of novel candidates within the Euphorbia plants to induce proliferation and apoptosis in human lymphocytes, mainly in CD3(+) T cells.

A role for a Hevea latex lectin-like protein in mediating rubber particle aggregation and latex coagulation

An in vitro aggregation of washed lutoid membrane and rubber particles, respectively, prepared from the bottom (lutoid) fraction and rubber layer of centrifuged fresh latex, leading to the formation of rubber coagulum necessary for a latex coagulation was demonstrated. A Triton X-100 extract of washed lutoid membrane proteins, isolated and prepared from the bottom fraction of centrifuged fresh latex was examined for its role in the latex coagulation process. It induced agglutination of rabbit erythrocytes, indicating the presence of a lectin-like protein. Hevea latex lectin-like protein (HLL) was purified to homogeneity by active chitin binding separation, followed by DEAE-Sepharose chromatography. Its M(r) analyzed by SDS-PAGE was 17 kDa, whereas that determined by gel filtration was 267 kDa. The HLL had a pI value of 7.2. Several glycoproteins were shown to inhibit the HLL-induced hemagglutination. The hemagglutinin activity of HLL was enhanced by Ca(2+). Of most interest was the finding that HLL strongly induced aggregation of the Hevea latex rubber particles (RP). This strong RP aggregation leads to latex coagulation, indicating the possibility that it is involved in the formation of the coagulum that plugs the latex vessel ends and stops the flow of latex upon tapping. In addition, the purified HLL also induced aggregation of RP taken from several other non-Hevea latex producing plants. This might indicate either a common or universal role of this lectin-like protein in RP aggregation and hence latex coagulation. This paper, for the first time, provides clear and unequivocal evidence for either a key biological role or physiological function of an endogenous latex lectin-like protein in the sequential process of latex coagulation.

Fine carbohydrate recognition of Euphorbia milii lectin

Glycans are key structures involved in biological processes such as cell attachment, migration, and invasion. Information coded on cell-surface glycans is frequently deciphered by proteins, as lectins, that recognize specific carbohydrate topology. Here, we describe the fine carbohydrate specificity of Euphorbia milii lectin (EML). Competitive assays using various sugars showed that GalNAc was the strongest inhibitor, and that the hydroxyl axial position of C4 and acetamido on C2 of GalNAc are critical points of EML recognition. A hydrophobic locus adjacent to GalNAc is also an important region for EML binding. Direct binding assays of EML revealed a stereochemical requirement for a structure adjacent to terminal GalNAc, showing that GalNAc residue is a necessary but not sufficient condition for EML interaction. The capacity of EML to bind epithelial tumor cells makes it a potentially useful tool for study of some over-expressed GalNAc glycoconjugates.

Anti-cancer drug discovery and development in Brazil: targeted plant collection as a rational strategy to acquire candidate anti-cancer compounds

Throughout medical history, plant products have been shown to be valuable sources of novel anti-cancer drugs. Examples are the VINCA: alkaloids, the taxanes, and the camptothecins, derived from the Madagscan periwinkle plant Catharantus roseus, the Pacific yew Taxus brevifolia, and the Chinese tree Camptotheca acuminata, respectively. For this reason, the South-American Office for Anti-Cancer Drug Development has implemented a large-scale project of acquisition and testing of compounds isolated from South American medicinal plants. The species are selected on the basis of a potentially useful phytochemical composition by consulting ethnopharmacological, chemosystemic, and ecological information. The collected samples are dried and first extracted with an organic solvent, then with distilled water. These crude extracts are evaluated at a concentration of 50 microg/ml for antiproliferative activity against one cell line. Extracts that significantly inhibit the growth of the cells (>/=50%) at relatively low concentrations (</=50 microg/ml) are submitted to the more comprehensive disease-oriented screen of the U.S. National Cancer Institute. In parallel, these samples are further purified by bioassay-guided purification, involving repeated fractionation by diverse chromatography methods. If the active substance is expected to represent a novel structure, it is identified by appropriate chemical techniques, mechanistic studies are performed with a wide diversity of tumor models and laboratory techniques, and efforts are undertaken for the synthesis of potentially more useful analogs.