**12. Biological role**

160 Antimicrobial Agents

chromatography, and gel filtration chromatography. In 2004 had a research that used affinity chromatography to purify the lectin from human serum proteins by Concanavalin A sepharose column coupled to two-dimensional gel electrophoresis. The purified sample had 2 fractions before use this technique (Rodriguez-Pineiro et al., 2004). Next year, a lectin from the marine red alga *Gracilaria ornata* (*Gracilariaceae, Rodophyta*); GOL was purified by 2 steps chromatography technique consist of ion exchange chromatography on DEAE-cellulose and affinity chromatography on mucin-Sepharose 4B. The GOL significantly affected the development of *Callosobruchus maculatus* larvae, indicating the possibility of using this lectin in a biotechnological strategy for insect management of stored cowpea seeds. (Leite et al., 2005). In 2007 Shi et al. study lectin from raw and canned red kidney bean (*Phaseolus vulgaris*). They used gel filtration technique to purify. Use Affi-gel Blue gel sepharose compare to thyroglobulin-Sepharose to purify the lectin from red kidney bean. Found that

the lectin from thyroglobulin more purify than Affi-gel Blue gel (Shi et al., 2007).

(for a more complete listing of recombinant plant lectins) (Streicher and Sharon, 2003).

Many lectin-containing plants are common constituents of the diet of humans and farm animals. Since lectins are known to act on cells in a variety of ways, such as agglutination, mitogenic stimulation and killing, and they are often resistant to heat and proteolytic enzymes, including those of intestinal bacteria, the effects of consumption of these proteins deserve special consideration. For many years it has been known that they occur in legumes such as soybeans, kidney beans, lima beans, mung beans, lentils, garden peas and peanuts that are a major food source for humans and animals in one part of the world. Although lectin containing foods are frequently consumed in cooked or otherwise processed form, such treatments may not always be adequate to completely inactivate the lectins present. Thus, lectins have been detected in roasted peanuts (Wang et al., 1999). Slow cooking of beans, without boiling, does not always eliminate lectin activity as observed with kidney beans cooked for 11 hr at 82 oC or for 5 hr at 91 oC. The stability of plant lectins in the stomach is evidenced, for example, by the finding that when Concanavalin A, PHA or WGA were intragastrically administered into rats between 50 and 90% of the lectin was recovered after 1 hr from the stomach by homogenizing the tissue in phosphate-buffered saline containing the appropriate specific sugar. Moreover, in the few experiments with humans that ate lectin-containing foods, namely tomatoes (Kilpatrick et al., 1985), red kidney beans (Pusztai et al., 1989) or peanuts, either raw or roasted (Wang et al., 1999) the lectins have not only withstood the acidity and the proteolytic enzymes of the intestinal tract, but a

**11. Lectins in edible plants** 

An alternative approach for the preparation of lectins has been made possible by the advent of recombinant DNA technology. It is based on the isolation of the cDNA or genomic DNA of the lectin, its insertion into a suitable vector and expression in an appropriate host cell. Isolation of the cDNA requires knowledge of at least part of the primary sequence of the lectin itself or of a structurally similar one. By this technique, several plant lectins, among them of pea (Stubbs et. al., 1986; and Van Eijsden et al., 1992), *Erythrina corallodendron* (Arango et al., 1993), peanut (Sharma and Surolia, 1994) and *Griffonia simplicifolia* (Zhu et al., 1996) have been expressed in *Escherichia coli*. Expression of plant lectins was also achieved in other systems, e.g. WGA in *Saccharomyces cerevisiae* (Nagahora et al., 1992), PHA and GNA in *Pichia pastoris* (Raemaekers et al., 1999), PNA in insect cells (Kumar et al., 1999) and SBA in monkey cells (Adar et al., 1997); Lectins are present abundantly in many plants. Despite this abundance, their precise biological roles in the plants to which they belong, are not well understood. The available evidences suggest two main roles for them.

### **12.1 Mediation of symbiotic relationship between nitrogen fixing microorganisms, primarily, rhizobia and leguminous plants**

Lectins localized at the root hairs are the entry sites for rhizobia. The lectins then aggregate the rhizobia in the root nodules and make them immobile (Hamblin and Kent, 1973; Bohlool and Schmidt, 1974; Diaz et al., 1989; Brewin and Kardailsky, 1997; and Hirsch, 1995). Type specificity of host-parasite interactions between leguminous plants and particular strains of rhizobia infecting them is determined by lectins. The expression of the pea lectin gene in white clover roots enabled them to be nodulated by a rhizobium strain specific for the pea plant (Van Eijsden et al., 1995).
