Polygonatum cyrtonema lectin (PCL) has been drawing rising attention due to its remarkable bioactivities. Whereas, large-scale isolation and purification of PCL from Polygonatum cyrtonema Hua is not feasible due to the extremely low propagation rate of this plant. Herein, an alternative method to produce large amount of PCL by Escherichia coli expression system was proposed, and recombinant Polygonatum cyrtonema lectin (rPCL) was successfully obtained under the optimized conditions (OD600=0.6, 30◦C, 0.5mM IPTG, pH 7.2). Subsequent SDS-PAGE and MALDI-TOF analysis confirmed that the molecular mass of rPCL was approximate to 12 kDa. After further identification of rPCL by Western blot and N-terminal amino acid sequence analysis, the comparisons of hemagglutinating and carbohydrate-binding activities as well as the anti-viral and apoptosis-inducing properties between rPCL and native Polygonatum cyrtonema lectin (nPCL) were made. It was verified that the bioactivities of rPCL were relatively weaker than that of nPCL. Moreover, for future exploring three-dimensional structure and structure–bioactivity relationship of rPCL, circular dichroism and fluorescence spectroscopy, preliminary crystallization and X-ray diffraction were determined. Taken together, these findings provide novel evidence that rPCL could replace nPCL as a potential anti-tumor and anti-viral protein in possible medical application and large-scale pharmaceutical industry.

Polygonatum cyrtonema lectin (PCL), a mannose/sialic acid-binding lectin, has been reported to display remarkable anti-proliferative and apoptosis-inducing activities toward a variety of cancer cells; however, the precise molecular mechanisms by which PCL induces cancer cell death are still elusive. In the current study, we found that PCL could induce apoptosis and autophagy in murine fibrosarcoma L929 cells. Subsequently, we demonstrated that inhibition of Ras could promote L929 cell death, suggesting that RaseRaf signaling pathway plays the key negative regulator in PCL-induced apoptosis. And, we showed that Ras-Raf signaling pathway was also involved in PCL-induced autophagy as the negative regulator. In addition, we found that class I phosphatidylinositol 3-kinase (PI3K)eAkt signaling pathway could play the negative regulator in PCL-induced apoptosis and autophagy. Taken together, these results demonstrate that PCL induces murine fibrosarcoma L929 cell apoptosis and autophagy via blocking Ras-Raf and PI3KeAkt signaling pathways.

Polygonatum cyrtonema lectin (PCL), a mannose/sialic acid-binding plant lectin, has recently drawn a rising attention for cancer biologists because PCL bears remarkable anti-tumor activities and thus inducing programmed cell death (PCD) including apoptosis and autophagy in cancer cells. In this review, we focus on exploring the precise molecular mechanisms by which PCL induces cancer cell apoptotic death such as the caspase-dependent pathway, mitochondria-mediated ROS-p38-p53 pathway, Ras-Raf and PI3K-Akt pathways. In addition, we further elucidate that PCL induces cancer cell autophagic death via activating mitochondrial ROS-p38-p53 pathway, as well as via blocking Ras-Raf and PI3K-Akt pathways, suggesting an intricate relationship between autophagic and apoptotic death in PCL-induced cancer cells. In conclusion, these findings may provide a new perspective of Polygonatum cyrtonema lectin (PCL) as a potential anti-tumor drug targeting PCD pathways for future cancer therapeutics.

The Galanthus nivalis agglutinin (GNA)-related lectin family exhibit significant anti-HIV and anti-HSV properties that are closely related to their carbohydratebinding activities. However, there is still no conclusive evidence that GNA-related lectins possess anti-influenza properties. The hemagglutinin (HA) of influenza virus is a surface protein that is involved in binding host cell sialic acid during the early stages of infection. Herein, we studied the 3D-QSARs (three-dimensional quantitative structure-activity relationships) of lectin-and HA-sialic acid by molecular modeling. The affinities and stabilities of lectin-and HA-sialic acid complexes were also assessed by molecular docking and molecular dynamics simulations. Finally, anti-influenza GNA-related lectins that possess stable conformations and higher binding affinities for sialic acid than HAs of human influenza virus were screened, and a possible mechanism was proposed. Accordingly, our results indicate that some GNA-related lectins, such as Yucca filamentosa lectin and Polygonatum cyrtonema lectin, could act as drugs that prevent influenza virus infection via competitive binding. In conclusion, the GNArelated lectin family may be helpful in the design of novel candidate agents for preventing influenza A infection through the use of competitive combination against sialic acid specific viral infection.

Galanthus nivalis agglutinin (GNA)-related lectin family, a superfamily of strictly mannose-binding specific lectins, has been well-known to possess several biological functions including apoptosis-inducing activities. However, the precise mechanisms of GNA-related lectins to induce apoptosis remains to be clarified. In this study, we showed that Polygonatum cyrtonema lectin (PCL) and Ophiopogon japonicus lectin (OJL), the two mannose-binding GNA-related lectins, could induce murine fibrosarcoma L929 cell apoptosis. In addition, we found that there was a close link between their sugar-binding and apoptosisinducing activities. Interestingly, we further confirmed that the mechanism of lectin-induced apoptosis was a caspase-dependent pathway. Moreover, we found that the two lectins could amplify tumor necrosis factorα (TNFα)-induced apoptosis. Taken together, these findings would open a new perspective for GNA-related lectins as potential anti-tumor agents.