**4. Occurrence and distribution**

Lectins are usually considered as a very large and heterogeneous group of proteins (Goldstein and Poretz, 1986). Although, there is no doubt indeed that numerous plant species of different taxonomic groupings contain lectins. The total number of welldocumented cases is about 400. Assuming that all the close relatives of these plants also contain agglutinins and that some new lectins will be discovered in the future, the expected occurrence of lectins is still limited to a small fraction of the plant kingdom. It can be concluded, therefore, that the occurrence of at least the classical agglutinating lectins in plants is the exception rather than the rule. However, in contrast to the relative scarcity of the agglutinating lectins, chimerolectins belonging to the Class I chitinases seem to be present in almost all plant species (Collinge et al., 1993).

Lectins are widely distributed throughout the plant kingdom where they have been found in a variety of tissues of a large number of different plants. In plants, lectins are particularly localized in seeds. Howard et al., 1972, reported that seed lectins are particularly seen in cotyledons where they appear during the later stages of maturation of the seeds. In addition to cotyledons, in some cases appreciable amounts of lectins have been reported in the embryos and small amounts in the seed coats (Pueppke et al., 1978). Immunolocalization studies have revealed that lectins are primarily found in the protein bodies of the cotyledon cells (Herman and Shannon, 1984). During the early seedling growth, Weber and Neumann (1980) noticed the decrease in lectin concentration as the cotyledons are resorbed. A short survey of the occurrence and concentration of lectins in seeds as well as in different types of vegetative tissues reveals striking differences in the location and relative abundance of the individual lectins. Usually, seed lectins are confined to cotyledons (e.g. legumes) or endosperm (e.g. castor bean). Normally lectins account for up to 5% of the total seed proteins. Sometimes, they become predominant protein in the seed representing 50% of the total seed protein (e.g. Phaseolus species). The non-seed lectins are found in all kinds of vegetative tissues such as leaves, stem, bark, bulb, tubers, corns, rhizomes, roots, fruits, flowers, ovaries, phloem sap and even in nectar (Peumans and Van Damme, 1995) and are only minor, quantitatively unimportant proteins. Non-seed lectins may occur in different tissues of the same plant. The snowdrop and daffodil lectins, for instance, have been found in all vegetative tissues, although the lectin is most abundant in the bulbs (Van Damme and Peumans, 1990). Similarly, the potato lectin occurs in tubers, stems, leaves and fruits (Kilpatrick, 1980). There are exceptions also. The ground elder berry lectin is confined to the rhizome only (Peumans et al., 1985). In the case of tulip bulbs, lectins are present in large quantities in the bulb but are almost undetectable in stem and leaves (Van Damme and Peumans, 1995). Some legume lectins are found in seeds as well as in bark tissues. A thorough examination of the genes coding for these lectins revealed that the seed and bark lectins are encoded by different, though highly hommologus, genes (Van Damme et al., 1995).

#### **5. Hemagglutinating activity by plant lectins**

Lectins are a group of protein that can bind to carbohydrate (which can be in form of sugar, oligosaccharide, or polysaccharide) specifically. Binding of the lectins is differed from those enzymes, anti-lectin antibodies, and other carbohydrate specific binding protein on that they will never change any bound-carbohydrate properties, not convert such carbohydrate to other substances, not come form immune origin, and being reversible binding. In addition to

Antimicrobial Activity of Lectins from Plants 151

Although the lectins have been found in human, animal, plant, and microorganisms, but it looks like that plant lectins were the most investigated for details (Sharon and Lis, 2001; and Chandra et al., 2006). Most lectins are present in seed cotyledons of the plant (but also found in any other parts such as roots, stems, rhizomes, and leaves in lesser amounts). In such tissues, most lectins are located within cytoplasm or protein bodies inside the cells (Moreira et al., 1991). In general, the lectins with the same ligand specificity contain different binding abilities mainly depended on their sources meant different genetic material that produce different lectins with different in three dimension structures. For instances, Tipthara et al., (2007) successfully purified a mannose specific lectin with strong rabbit hemagglutinating activity (0.017 μg of minimum amount that hemagglutination presented) of from *Curcuma Zedoaria*, Thipthara et al., (2008) also purified many lectins with weak activity (0.140 to 0.190 mg minimum amount that hemagglutination presented), Wong et al., (2008) purified mannose/glucose specific lectin with extremely strong activity (83.063 ng minimum amount that hemagglutination presented) from *Castanopsis chinensis*. Most of plant lectins become a set of important tools for glycobiology achievements. They are also applied in detection, isolation, and characterization of glycoconjugated substances mainly in glycoprotein, proteoglycan, and modified polysaccharides (Sharon and Lis, 2001). The lectins are also advantages in immunology, histochemistry, pathology, and physiology areas. One familiar instance which the lectin usage is clearly seen is ABO blood type identification using blood group specific lectin such as Concanavalin A, a lectin derived from jack bean seed (*Canavalia ensiformis*) that can specifically bind to non-reducin α-terminal mannose. This blood groups determination is based on presence or absence of specific glycoprotein on red blood cells that the lectins can bind and make red blood cells agglutination (Moreira et al., 1991) by forming network with red blood cells and then can not be collected as button like form in the U shape bottom well. From this incident, a method widely used for lectin screenings or characterizations mainly involved cells agglutination, especially red blood cells from various animals (Sharon and Lis, 2001). The lectins also have other roles in mammals. There was evidences indicated that the lectins played the important roles in cell differentiation, cell movement and phagocytosis, cell to cell and cells to matrix substances communication,

cell organization in tissues, and embryo morphogenesis (Moreira et al., 1991).

from 0.18 to 0.70 μg/ ml for HHA depended on tested viral nature.

On the other hand, consuming of lectins also may cause adverse results in some cases. Several lectins such as Concanavalin A and wheat germ agglutinin (WGA) are toxic to mammalian cells, but relatively low compared with other toxic substances such as approximately 1000 times lower than ricin (an toxic albumin from Caster bean). It is believed that production and accumulation of toxic lectins in some plants are a kind of defending mechanisms which plants develop for protecting them form certain plant eating organisms such as insects and mammals (Peumans and Van Damme, 1995) and plant pathogens. Aside from defense mechanisms, the lectins also have their essential roles in plant-microorganism symbiosis, cell differentiation, pollen recognition, cell wall elongation, and as a reserved protein (Moreira et al., 1991). Interestingly, some plant lectins were found to be well react with viral surface glycoprotein and were hoped to use in controlling many diseases originated from viruses which current methods are still inadequate controllable efficiencies. Balzarini et al., (2004) isolated two mannose-specific lectins from *Galanthus nivalis* (snowdrop) (GNA) and *Hippeastrum* sp. hybrid (Amaryllis) (HHA) and found that they contained *in vitro* anti-HIV virus activities ranged from 0.12 to 1.2 μg/ ml for GNA and

carbohydrate binding specifically, the lectins can cause cells agglutinated and glycoprotein or carbohydrate precipitated. That is why the lectins are sometimes called "agglutinin" (Sharon and Lis, 2001). Since most lectins have two or more carbohydrate binding sites in their molecules, which can make cross-linkages between cells or carbohydrate containing molecules and form solid network. However, there are also some certain lectins that presented in momovalent binding site, and thus can not agglutinate cells or precipitate carbohydrate.

Some lectins contain more than one type of acting site or one activity in single molecules so that they can bind to carbohydrate and can exhibit other behaviors such as enzymatic activity (which make this lectin called "lectzyme"), mitogenic activity, and transportation activity in the same time. From these phenomena, the lectins can be classified into three types according to their acting sites as "merolecins" (the lectins with only single carbohydrate binding domain, usually small single peptides), "hololectins" (the lectins with two resemble carbohydrate binding domains), "chimerolectins" (the lectins contains both carbohydrate binding domain and other well-defined biological active domains which act dependently of previous domain). Beside this classification, the lectins can also be classified by their ligand specificities in two manners. The first is that by sizes of binding ligand which the lectins can be divided into two group; the lectins that specifically binding to monosaccharides as well as oligosaccharides and the lectins that specifically binding to only oligosaccharides (Peumans and Van Damme, 1995). The second classification manner is relatively old style that was set up during little details of lectin's information known. Thus, they were separated by their legand specificity only in sugar types such as mannose or glucose specific lectins, galactose specific lectins, and sialic acid specific lectins. However, they were recently found that most lectins tended to recognize certain three dimension structure than monosaccharide specificity. Thus, this classification style may not up to date because many of lectins formally grouped in one class are now no longer suitable for such class. Anyways, it may be familiar to some authors and may also found in some present documents.

Fig. 1. Schematic representation of the three types of plant lectins: merolectins, hololectins, and chimerolectins. (Peumans and Van Damme, 1995).

carbohydrate binding specifically, the lectins can cause cells agglutinated and glycoprotein or carbohydrate precipitated. That is why the lectins are sometimes called "agglutinin" (Sharon and Lis, 2001). Since most lectins have two or more carbohydrate binding sites in their molecules, which can make cross-linkages between cells or carbohydrate containing molecules and form solid network. However, there are also some certain lectins that presented in momovalent binding site, and thus can not agglutinate cells or precipitate carbohydrate.

Some lectins contain more than one type of acting site or one activity in single molecules so that they can bind to carbohydrate and can exhibit other behaviors such as enzymatic activity (which make this lectin called "lectzyme"), mitogenic activity, and transportation activity in the same time. From these phenomena, the lectins can be classified into three types according to their acting sites as "merolecins" (the lectins with only single carbohydrate binding domain, usually small single peptides), "hololectins" (the lectins with two resemble carbohydrate binding domains), "chimerolectins" (the lectins contains both carbohydrate binding domain and other well-defined biological active domains which act dependently of previous domain). Beside this classification, the lectins can also be classified by their ligand specificities in two manners. The first is that by sizes of binding ligand which the lectins can be divided into two group; the lectins that specifically binding to monosaccharides as well as oligosaccharides and the lectins that specifically binding to only oligosaccharides (Peumans and Van Damme, 1995). The second classification manner is relatively old style that was set up during little details of lectin's information known. Thus, they were separated by their legand specificity only in sugar types such as mannose or glucose specific lectins, galactose specific lectins, and sialic acid specific lectins. However, they were recently found that most lectins tended to recognize certain three dimension structure than monosaccharide specificity. Thus, this classification style may not up to date because many of lectins formally grouped in one class are now no longer suitable for such class. Anyways, it

may be familiar to some authors and may also found in some present documents.

**Hevein**

**Melolectin Hololectin Chimerolectin**

**Concanavalin A**

Fig. 1. Schematic representation of the three types of plant lectins: merolectins, hololectins,

**Superlectin**

**TxLC-I**

and chimerolectins. (Peumans and Van Damme, 1995).

**Ricin**

**Binding site**

Although the lectins have been found in human, animal, plant, and microorganisms, but it looks like that plant lectins were the most investigated for details (Sharon and Lis, 2001; and Chandra et al., 2006). Most lectins are present in seed cotyledons of the plant (but also found in any other parts such as roots, stems, rhizomes, and leaves in lesser amounts). In such tissues, most lectins are located within cytoplasm or protein bodies inside the cells (Moreira et al., 1991). In general, the lectins with the same ligand specificity contain different binding abilities mainly depended on their sources meant different genetic material that produce different lectins with different in three dimension structures. For instances, Tipthara et al., (2007) successfully purified a mannose specific lectin with strong rabbit hemagglutinating activity (0.017 μg of minimum amount that hemagglutination presented) of from *Curcuma Zedoaria*, Thipthara et al., (2008) also purified many lectins with weak activity (0.140 to 0.190 mg minimum amount that hemagglutination presented), Wong et al., (2008) purified mannose/glucose specific lectin with extremely strong activity (83.063 ng minimum amount that hemagglutination presented) from *Castanopsis chinensis*. Most of plant lectins become a set of important tools for glycobiology achievements. They are also applied in detection, isolation, and characterization of glycoconjugated substances mainly in glycoprotein, proteoglycan, and modified polysaccharides (Sharon and Lis, 2001). The lectins are also advantages in immunology, histochemistry, pathology, and physiology areas. One familiar instance which the lectin usage is clearly seen is ABO blood type identification using blood group specific lectin such as Concanavalin A, a lectin derived from jack bean seed (*Canavalia ensiformis*) that can specifically bind to non-reducin α-terminal mannose. This blood groups determination is based on presence or absence of specific glycoprotein on red blood cells that the lectins can bind and make red blood cells agglutination (Moreira et al., 1991) by forming network with red blood cells and then can not be collected as button like form in the U shape bottom well. From this incident, a method widely used for lectin screenings or characterizations mainly involved cells agglutination, especially red blood cells from various animals (Sharon and Lis, 2001). The lectins also have other roles in mammals. There was evidences indicated that the lectins played the important roles in cell differentiation, cell movement and phagocytosis, cell to cell and cells to matrix substances communication, cell organization in tissues, and embryo morphogenesis (Moreira et al., 1991).

On the other hand, consuming of lectins also may cause adverse results in some cases. Several lectins such as Concanavalin A and wheat germ agglutinin (WGA) are toxic to mammalian cells, but relatively low compared with other toxic substances such as approximately 1000 times lower than ricin (an toxic albumin from Caster bean). It is believed that production and accumulation of toxic lectins in some plants are a kind of defending mechanisms which plants develop for protecting them form certain plant eating organisms such as insects and mammals (Peumans and Van Damme, 1995) and plant pathogens. Aside from defense mechanisms, the lectins also have their essential roles in plant-microorganism symbiosis, cell differentiation, pollen recognition, cell wall elongation, and as a reserved protein (Moreira et al., 1991). Interestingly, some plant lectins were found to be well react with viral surface glycoprotein and were hoped to use in controlling many diseases originated from viruses which current methods are still inadequate controllable efficiencies. Balzarini et al., (2004) isolated two mannose-specific lectins from *Galanthus nivalis* (snowdrop) (GNA) and *Hippeastrum* sp. hybrid (Amaryllis) (HHA) and found that they contained *in vitro* anti-HIV virus activities ranged from 0.12 to 1.2 μg/ ml for GNA and from 0.18 to 0.70 μg/ ml for HHA depended on tested viral nature.

Antimicrobial Activity of Lectins from Plants 153

Broadly reveal, lectins can be divided into those that bind monosaccharides as well as oligosaccharides, and those that recognize oligosaccharides only (Wu et al., 2001). It is noteworthy that almost all saccharides recognized by lectins are typical constituents of animal cell surfaces. This is perhaps a reflection of the method commonly used for lectin detection (Tsivion and Sharon, 1981), as a result of which lectins recognizing sugars not

A lectin with specificity for mannose and glucose residues has been isolated in crystalline form the fava bean (*Vicia laba*) by a procedure which included absorption to Sephadex. It has a molecular weight of 50,000 Da and appears to be a tetramer made of two subunits of 18,000 Da and two subunits of 9,000 Da. These studies determine amino acid sequence and three-dimensional structure of lectin were similar with structural features of Concanavalin

Fig. 2. Common structural features of *N*-acetylneuraminic acid and *N*-acetylglucosamine (A) and of mannose and fucose (B). Similarity of *N*-acetylglucosamine and *N*-acetylneuraminic acid at positions C-2 (acetamido) and C-3 (hydroxyl) of the pyranose ring is observed when the sialic acid molecule is suitably rotated. Rotation of the fucose molecule by 180 Å allows superimposition of its ring oxygen, 4-OH, 3-OH and 2-OH with the ring oxygen, 2-OH, 3- OH and 4-OH of mannose, respectively. Groups that thus occupy the same positions in

*N***-Acetyl-D-glucosamine L-Fucose** 

**7. Sugar binding activity and specificity of plant lectins** 

present on erythrocytes might have been overlooked.

**O**

**A B**

**NHAc**

**O**

**NHAc OH**

**<sup>C</sup> <sup>H</sup> C**

**CH2OH OH**

*N***-Acetylneuraminic acid D-mannose** 

**HO**

**4**

**HO**

**3**

**HO**

**2**

**HO**

**3**

**HOH2C**

**HO**

**O**

**O**

**OH**

**4**

**2**

**OH**

**CH3**

**OH**

**HO**

**H**

**7.1 Mannose/glucose** 

space are underlined. (Sharon, 1993).

A (Irvin, 1976).

**HO**

**HO**

**HO**

**HO**

**HO**

**HOH2C**

**COOH**
