Expression and characterization of two domains of Pinellia ternata agglutinin (PTA), a plant agglutinin from Pinellia ternata with antifungal activity

Lectins, Interconnecting Proteins with Biotechnological/Pharmacological and Therapeutic Applications

Lectins are proteins extensively used in biomedical applications with property to recognize carbohydrates through carbohydrate-binding sites, which identify glycans attached to cell surfaces, glycoconjugates, or free sugars, detecting abnormal cells and biomarkers related to diseases. These lectin abilities promoted interesting results in experimental treatments of immunological diseases, wounds, and cancer. Lectins obtained from virus, microorganisms, algae, animals, and plants were reported as modulators and tool markers in vivo and in vitro; these molecules also play a role in the induction of mitosis and immune responses, contributing for resolution of infections and inflammations. Lectins revealed healing effect through induction of reepithelialization and cicatrization of wounds. Some lectins have been efficient agents against virus, fungi, bacteria, and helminths at low concentrations. Lectin-mediated bioadhesion has been an interesting characteristic for development of drug delivery systems. Lectin histochemistry and lectin-based biosensors are useful to detect transformed tissues and biomarkers related to disease occurrence; antitumor lectins reported are promising for cancer therapy. Here, we address lectins from distinct sources with some biological effect and biotechnological potential in the diagnosis and therapeutic of diseases, highlighting many advances in this growing field.

Purification of a mannose-binding lectin Pinellia ternata agglutinin and its induction of apoptosis in Bel-7404 cells

A novel high-throughput purification method for a monocot mannose-binding lectin, Pinellia ternata agglutinin (PTA), from tubers of P. ternata was established by mannose-Sephrose 4B affinity chromatography. The total protein was extracted from tubers of P. ternata using phosphate buffered saline (PBS) buffer. The extracted total protein was precipitated completely at 65% ammonium sulfate saturation and dissolved in different concentrations of NaCl solution to activate its binding affinity toward the column. PTA was bound to the affinity column by loading of the total protein into the column and elution using PBS buffer. The maximum purification yield (35.5mg/g) was obtained when PTA was treated with 25% (w/v) NaCl solution, and the purity of PTA analyzed by SDS-PAGE was ∼97%. The agglutination property of purified PTA was confirmed by mouse erythrocytes, which indicates its biological function. Nuclear staining assay and DNA fragmentation demonstrated that PTA could induce apoptosis of Bel-7404 cells, which further demonstrates its biological and pharmacological activities. Induction of apoptosis in the human tumor Bel-7404 cell line by PTA indicates its possible use in cancer therapy. The present investigation reports a significantly improved isolation method to obtain highly purified mannose-binding plant lectin proteins. The proposed method has great potential for industrial application because of its advantages, which include rapid isolation, high purity, high yield, low cost, and minimal requirement of chemical materials.

Prokaryotic expression and bioactivity analysis of N-terminus domain of Pinellia ternata agglutinin using alkaline phosphatase signal peptide

Pinellia ternata agglutinin (PTA) from the tubers of P. ternata is a two-domain monocot mannose-binding lectin. Pta-n encoding N-terminus domain of PTA (PTA-N) was fused with Escherichia coli alkaline phosphatase signal peptide (APSP) gene by polymerase chain reaction (PCR) for secretion expression. The fused nucleotide sequence apsp-pta-n was inserted into pET-28a prokaryotic expression vector by restriction enzyme digest sites (Nco I and Xho I), and then overexpressed in E. coli BL21(DE3) cells by isopropyl β-d-1-thiogalactopyranoside (IPTG) induction. Expressed APSP targeted the recombinant protein APSP-PTA-N into the periplasmic space, and then APSP was recognized and automatically cleaved by the membrane-bound signal peptidase. Ni-NTA chromatography was used for the purification and about 20 mg/L purified PTA-N was obtained. The minimum agglutination concentration of PTA-N determined by mice erythrocytes was 6.33 ± 0.47 μg/ml. The carbohydrate inhibition assay was carried out to determine the carbohydrate-binding property indicating PTA-N bound to specific sugars. The in vitro anti-proliferative activity towards human tumor cell lines and anti-fungal activity against Gibberella saubinetii were also demonstrated. Nuclear staining assay was performed to demonstrate PTA-N induced cell apoptosis. The results showed that PTA-N had significant biological functions, similar to native PTA. This strategy was the first time used to express plant mannose-binding lectin proteins and the product induced human tumor cell apoptosis, suggesting its potential application in biomedicine research.

Pinellia ternata agglutinin expression in chloroplasts confers broad spectrum resistance against aphid, whitefly, Lepidopteran insects, bacterial and viral pathogens

Broad spectrum protection against different insects and pathogens requires multigene engineering. However, such broad spectrum protection against biotic stress is provided by a single protein in some medicinal plants. Therefore, tobacco chloroplasts were transformed with the agglutinin gene from Pinellia ternata (pta), a widely cultivated Chinese medicinal herb. Pinellia ternata agglutinin (PTA) was expressed up to 9.2% of total soluble protein in mature leaves. Purified PTA showed similar hemagglutination activity as snowdrop lectin. Artificial diet with purified PTA from transplastomic plants showed marked and broad insecticidal activity. In planta bioassays conducted with T0 or T1 generation PTA lines showed that the growth of aphid Myzus persicae (Sulzer) was reduced by 89%-92% when compared with untransformed (UT) plants. Similarly, the larval survival and total population of whitefly (Bemisia tabaci) on transplastomic lines were reduced by 91%-93% when compared with UT plants. This is indeed the first report of lectin controlling whitefly infestation. When transplastomic PTA leaves were fed to corn earworm (Helicoverpa zea), tobacco budworm (Heliothis virescens) or the beet armyworm (spodoptera exigua), 100% mortality was observed against all these three insects. In planta bioassays revealed Erwinia population to be 10,000-fold higher in control than in PTA lines. Similar results were observed with tobacco mosaic virus (TMV) challenge. Therefore, broad spectrum resistance to homopteran (sap-sucking), Lepidopteran insects as well as anti-bacterial or anti-viral activity observed in PTA lines provides a new option to engineer protection against biotic stress by hyper-expression of an unique protein that is naturally present in a medicinal plant.