A Lectin with Highly Potent Inhibitory Activity toward Breast Cancer Cells from Edible Tubers of Dioscorea opposita cv. Nagaimo

Yau Sang Chan,Tzi Bun Ng,Asad U Khan

doi:10.1371/journal.pone.0054212

Abstract

A 70-kDa galactose-specific lectin was purified from the tubers of Dioscorea opposita cv. nagaimo. The purification involved three chromatographic steps: anion exchange chromatography on a Q-Sepharose column, FPLC-anion exchange chromatography on a Mono Q column, and FPLC-gel filtration on a Superdex 75 column. The purified nagaimo lectin presented as a single 35-kDa band in reducing SDS-PAGE while it exhibited a 70-kDa single band in non-reducing SDS-PAGE suggesting its dimeric nature. Nagaimo lectin displayed moderate thermostability, retaining full hemagglutinating activity after heating up to 62°C for 30 minutes. It also manifested stability over a wide pH range from pH 2 to 13. Nagaimo lectin was a galactose-specific lectin, as evidenced by binding with galactose and galactose-containing sugars such as lactose and raffinose. The minimum concentration of galactose, lactose and raffinose required to exert an inhibitory effect on hemagglutinating activity of nagaimo lectin was 20 mM, 5 mM and 40 mM, respectively. Nagaimo lectin inhibited the growth of some cancer cell lines including breast cancer MCF7 cells, hepatoma HepG2 cells and nasopharyngeal carcinoma CNE2 cells, with IC50 values of 3.71 µM, 7.12 µM and 19.79 µM, respectively, after 24 hour treatment with nagaimo lectin. The induction of phosphatidylserine externalization and mitochondrial depolarization indicated that nagaimo lectin evoked apoptosis in MCF7 cells. However, the anti-proliferative activity of nagaimo lectin was not blocked by application of galactose, signifying that the activity was not related to the carbohydrate binding specificity of the lectin.

Highlights

Lectins are a group of proteins or glycoproteins possessing carbohydrate binding capability
Lectins are classified in accordance with their carbohydrate specificities: mannose binding [1], mannose and glucose binding [2], galactose binding [3], etc
The protocol contributed to purification of nagaimo lectin by approximately 33.4 folds (Table 1)

Summary

Introduction

Lectins are a group of proteins or glycoproteins possessing carbohydrate binding capability. Van Damme et al introduced another classification system of lectins, based on the structure of lectins, in which were classified into merolectins, hololectins, chimerolectins and superlectins [8]. They have classified plant lectins into 12 groups according to their structural and evolutionary relationships, such as legume lectins, jacalins, amaranthins [9,10]. Both animal and plant lectins exhibit a variety of biological activities. They are one of the best targets for identification and isolation of new plant lectins with a large yield, allowing extensive characterization of the lectins, helping to reveal their biological potentials (e.g. anti-tumor activities)

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Conclusion