Table of Contents  
REVIEW ARTICLE
Year : 2012  |  Volume : 4  |  Issue : 1  |  Page : 20-25

Biological role of lectins: A review


1 Department of Oral Pathology, SIBAR Institute of Dental Sciences, Guntur, Andhra Pradesh, India
2 Department of Oral Pathology, Lenora Institute of Dental Sciences, Rajamandry, Andhra Pradesh, India

Date of Web Publication10-Sep-2012

Correspondence Address:
K Kiran Kumar
Department of Oral Pathology, SIBAR Institute of Dental Sciences, Guntur, Andra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0975-8844.99883

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  Abstract 

Lectins comprise a stracturally vary diverse class of proteins charecterized by their ability to selectively bind carbohydrate moieties of the glycoproteins of the cell surface. Lectins may be derived from plants, microbial or animal sources and may be soluble or membrane bound. Lectins is a tetramer made up of four nearly identical subunits. In human, lectins have been reported to cause food poisoning, hemolytic anemia, jaundice, digestive distress, protein and carbohydrate malabsorption and type I allergies. The present review focuses on the classification, structures, biological significance and application of lectins.

Keywords: Lectins, Glycoproteins, Mycology


How to cite this article:
Kumar K K, Chandra K L, Sumanthi J, Reddy G S, Shekar P C, Reddy B. Biological role of lectins: A review. J Orofac Sci 2012;4:20-5

How to cite this URL:
Kumar K K, Chandra K L, Sumanthi J, Reddy G S, Shekar P C, Reddy B. Biological role of lectins: A review. J Orofac Sci [serial online] 2012 [cited 2017 May 23];4:20-5. Available from: http://www.jofs.in/text.asp?2012/4/1/20/99883


  Introduction Top


Lectins are carbohydrate binding proteins present in most of the plants and in some animals. [1] The word Lectins is derived from Latin-'Legree' = to pick or select. Lectins do not cause any antigenic stimulation within the immune system but they have the basic capacity to bind analogously to an antibody. [1]

These lectins selectively bind carbohydrate moieties of the glycoprotein that decorate the surface of most of the animal cells. Structurally, these lectins have a diverse class of proteins, which have the ability to bind carbohydrates with considerable specificity. [2] There are numerous studies which attempted to show the in-vivo and in-vitro effects of Lectins. In-vitro, they have been shown to effect lymphocyte mitogenesis, both stimulating and inhibitory effects, with the lymphocytes of Gastro Intestine Tract (GIT) being most susceptible. They possess the ability to aggregate immunoglobulin's, to trigger the alternative complement pathway, to inhibit fungal growth and also to induce histamine release from basophilic and mast cells. Lectins are relatively resistant to both heat (at 70°C more than 30 min) and digestion. Some of the lectins are highly resistant to gastric acid and proteolytic enzymes. [3]

Structure of lectins

According to Goldstein et al., [4] lectins are mainly made-up of carbohydrate binding proteins or glycoproteins of nonimmune origin which binds the cells or precipitates, glyco-conjugates or sometimes, both.

The specific capacity of lectins to bind with the cell surface mainly depends on the monosaccharides or simple oligosaccharides, which when present, inhibit the lectins associated reaction. In some instances, carbohydrate associated enzymes that have multiple combining sites will agglutinate or precipitate the glyco-conjugates and thus may be considered as lectins. [5]

Some lectins are structurally differentiated such as:

  1. Erythrine C lectins
  2. Concanavalin C lectins
  3. Ulex europaeus lectins
  4. C type lectins


Classifications

Generally lectins are classified into four groups, based on their affinity to bind with

  1. Glucose/mannose
  2. Galactose and N-acetyl-D-galactosamine
  3. L-fucose
  4. Sialic acids


Another classification of Lectins based on lectin-like proteins is-

Type I: Depending up on structural and evolutionary sequence similarities.

Type II: Depending up on proteins without established evolutionary.

In type I again, the following lectin types are present-

  1. Beta prism lectins (B type)
  2. Calcium dependent lectins (C type)
  3. Ficolins-Fibrinogen/collagen domain containing lectins (F type)
  4. Garlic and snow drop lectins (G type)
  5. Hyaluronin bonding proteins or hyal adherins (H type)
  6. Immunoglobulin superfamily lectins (I type)
  7. Jocob and related lectins (J type)
  8. Legume seed lectins (L type)
  9. Alpha mannosidease related lectins (M type)
  10. Nucleotide phosphohydrolases (N type)
  11. Racin lectin (R type)
  12. Tachypleus tridentatus (T type)
  13. Wheat germ agglutinin (W type)
  14. Xanopus egg lectins (X type)


Type II: Lectin-like proteins, without established evolutionary

  1. Annexins
  2. Pentraxins with pentavalent domain
  3. G-domains-glycans on alpha dextroglycan
  4. CD11b/CD 18 (beta integrins, CR3)-fungal glucans and exposed Glc NAC residues on Glycoproteins. [5]


Structures

The binding of Lectins is reversible and noncovalent with simple or complex carbohydrate conjugates, whether free in solution or on cell surfaces. The surface which contains glycoconjugates will only act as a lectins receptor. The specificity of lectins is generally based on hapten inhibition test in which various sugars will be tested for their capacity to inhibit hemagglutination of erythrocytes. All lectin molecules posses two or more carbohydrate binding sites, a property essential for their ability to agglutinate cells or to react with complex carbohydrates. The combining sizes of some lectins may accommodate up to five or more sugar residues. Many multi branched oligosaccharides exhibits stronger lectins binding reactivates than linear ones, because of cooperative binding effects of lectin and carbohydrate complexes. Some of the lectins possess dual or multiple affinities for different disaccharides. Binding between these molecules will be hydrophobic but electrostatic forces are rarely involved. Lectins have been purified from crude aqueous buffer or saline extracts of various tissues by standard methods associated with protein chemistry. These include ammonium sulfate or ethanol precipitation and the use of affinity chromatography. [6]

Source

Lectins were identified almost a century ago. Initially they were discovered in castor bean by Stillmark in 1888. [7] Boyd, in 1945 found that some of the lectins were blood type specific. He reported that lectins found in lime beans will agglutinate with blood type A. [8] Since that time lectins are observed in both plants and animals-particularly edible cereals, beans, nuts, and fishes, especially shell fishes. [8] Many specific lectins are identified in both plants and animals. Today lectins are commonly used in laboratories for blood typing, particularly type A1. [9]

Absorption

Many of the plants and animal lectins are resistant to both heating and digestion. Many of these lectins are highly stable, thermally (at 70°C for more than 30 min.), but these lectins do not completely degrade with cooking. Some of them are even relatively resistant to digestive enzymes and acids. While some of the lectins are degraded and others pass through the gut, about 1-5% are re-absorbed into the blood stream in animals, which is considered a significant amount, sufficient to cause an immune response. [2]

Biological role

The biological role of lectins is speculative. Lectins may be involved in sugar transport or carbohydrate storage. Some of the lectins may be associated with the binding of symbiotic rhizobia to form root nodules. Because of their proprietary role in adhesion and agglutination, lectins have been considered as important in both symbiotic and pathogenic interaction between some microorganisms and hosts. The microbial lectins may play an important role in adhesion to the surfaces colonized by the microorganisms. For example, tomato lectins binds to mucosal cells and resist denaturation by acids and by proteolytic enzymes. [10]

There are few studies which established lectins as agglutination specific for blood groups of erythrocytes. Due to their multifaceted biological properties, lectins were later developed by cell biologists as probes to investigate cell surface structures and functions. Some of the lectins have been used to fractionate animal cells including B and T lymphocytes and to demonstrate changes in cell surface architecture following virus infection or parasite infection. [11]

Lectins have been used as carrier for the delivery of chemotherapeutic agents. Lectins are significant reagents for investigating cell surface receptors in bacteria, protozoa, and higher organisms. The interactions of plant lectins with microorganisms have been applied for typing of bacteria, fungi, and protozoa. Lectins are useful for characterizing bacterial cell components and for detecting bacteriophage receptors. Many bacteria contain surface associated lectins that enable these microorganisms to adhere to surfaces. One of the major advantages of applying lectins in microbiology is that cellular or surface receptor sites can be partially characterized by hapten inhibition. [12]

Advantages

  • Stability
  • Activity in small concentration
  • Commercial availability of many lectins
  • Ability to probe subtle surface structural differences between various isolates [13]
Disadvantages

In humans, lectins have been reported to cause damage, including mass food poisoning from uncooked kidney beans and it also causes hemolytic anemia and jaundice from Mexican fava beans. Lectins may cause acute gastrointestinal symptoms including nausea and vomiting. They bind to the luminal surface of absorptive erythrocytes in the small intestines. This will cause severe damages to the microvilli of the intestine, thus disrupting the digestion and absorption.

  • Lectins can also promote the growth of harmful bacteria in the gut.
  • Lectins also disrupt proteins and carbohydrate malabsorption. In protein malabsorption, gut lectins bind to erythrocytes, causes inflammation which blocks the production of enterokinase, a protein enzyme. In case of carbohydrate malobsorption, it reduces intestinal glucose uptake by 50%. Wheat germ agglutinin and other lectins can even bind to insulin receptors on cells, disrupting glucose metabolism. Grains will have high content of lectins, which may cause inflammatory bowel and celiac diseases in human. [14]
Applications

Lectins can be used for diagnostic as well as for therapeutic purpose. Application of lectins can be grouped as:
  1. Lectins in tumor markers
  2. Lectins and odontogenic cysts and tumors
  3. Lectins in clinical microbiology
  4. Lectins in serology
  5. Lectins in food and human reaction
  6. Lectins in inflammation


Lectins as tumor markers

There are polyvalent proteins of nonimmune origin. Glycoproteins and glycolipids are the proteins present on the cell surface of squamous cells, which act as antigens. These markers will help in immunohistochemical (IHC) studies on skin or oral mucosa of human tissue. Skin or mucosa UEA-1 is the marker shown on the superficial cell layers. In all the epidermal layers, there will be more expression of Con -A, LCA, RAC-1 and WGA. The expression of GS-I, SBA, PWM and PNA, will be more restricted in its distribution in the IHC, on mucosal sections. This implies to the different staining patterns of these markers which express different degree of differentiation. In oral squamous cell carcinoma, PWM and PNA will be bound to those areas more markedly, where there is squamous cell differentiation, and GS-I mainly stains the cells which are not well differentiated. The same markers (GS-1) can be observed to be reliable markers for squamous metaplasia of hepatoid, perianal, and mammary gland tumors. On GS-I, PWM, and PNA are more reliable and further studies on tumor models are necessary. These lectin-binding profiles may be useful in differentiating benign and malignant tumors. [15]

Lectins and odontogenic cysts and tumors

Ulex europaeus agglutinin-I (UEA-I), Banderirea simplicifolia agglutinin I (BSA-I), and Peanut agglutinin (PNA) were used in odontogenic cysts and tumors. These lectins (UEA-I and BSA-I) are over expressed in nonneoplastic cysts, but some of the lectin groups will negatively stain for Ameloblastoma, whereas PNA binds markedly with keratinized tumors. In case of postoperative maxillary cysts, there will be changes in the glycoconjugate expression of the metaplastic lining epithelium. [16]

Lectins and dysplasia

Lectins will go and bind to noncarbohydrate ligands and shows reaction with nuclei. Few studies suggested that membrane bound carbohydrates may be essential for cellular differentiation and malignant transformation. In the epithelium, short structures of lectins are detected on the basal cells and longer structures are seen on more mature spinous cells. This sequential expression of lectins was observed to be more disturbed with increasing grade of epithelial dysplasia. [17]

Some lectins such as Jack fruit lectins (JFL) and PNA are used in detection of various clinico-pathological stages of tumor progression in the oral mucosa and also in the various other oral mucosal lesions. In nonkeratinizing epithelium, the spinous layer cells showed mild membrane staining, while normal keratinizing epithelium showed a moderate membrane staining and mild cytoplasmic staining in all the layers. In potentially malignant lesions such as leukoplakia, mild to moderate cytoplasmic staining was observed. Whereas in carcinomas, intensity of staining will increase and JFL showed significant correlation in both membranes and cytoplasm of all layers with different stages of tumor progression. PNA and JFL may be used as cytoplasmic probes in differentiating malignancy from benign lesions of the oral mucosa. [18]

Lectins and their clinical microbiological applications

Basic function of lectins is transport or carbohydrate storage. Lectins have been considered very important in both symbiotic and pathogenic interactions between microorganisms and hosts. These lectins will also mediate adhesion to the surface, colonized by microorganisms. [19]

Some of the lectins are significant reagents for identification of cell surface receptors in various bacteria, protozoa, and higher organisms. These lectins are used for typing bacteria, fungi, and protozoa [20] [Table 1] and [Table 2]. Bacterial lectins resemble plant lectins in carbohydrate specificity and relative thermo stability. [21]
Table 1: Lectin family and location and functions:

Click here to view
Table 2: How lectins have been used in clinical microbiology

Click here to view


Several bacterial species possess surface lectins that yield coaggregation responses with certain yeast cells. [22] Group B streptococci grown in selective and nonselective media such as Todd-Hewitt broth can be specifically detected by using tomato lectins. The growth of Beta streptococci will take 5 h on this broth. [23]

Lectins in mycobacterium

Sumner and Howell in 1936 observed that Concanavalin A had the capacity to agglutinate bacteria belonging to the genus mycobacterium. [22] Some studies on the inhibitory effects of lectins shows that they react with the nonreducing terminal, D-arabino-furanosyl residues situated at the end of arabino galacton. These findings can be visualized under fluorescent microscope. [24]

Lectins in mycology

Barkai-Golan and Sharon N studied on lectins, which can bind with fungal cell surface, and these lectins can be an important tool for classification of fungi. [25] Chitin, a polymer of beta (1->4) N-acetyl-D-glucosamine is one of the major component of the fungal cell wall, which binds with fluorescein-conjugated wheat germ agglutinin, a useful probe to detect chitin on the fungal cell wall. [26],[27]

This wheat germ agglutinin has also been shown to inhibit the growth and spore germination of the fungus trichoderma viridae. [28] Tkacz et al. in 1972 studied on Fluorescein-conjugated concanavalin A, which has the ability to bind with Saccharomyces cervisiae, but does not show any reaction with Schizosaccharomyces pombe, which could be because of the lack of alpha-mannans within the cell wall of S. pombe. [29]

Uses of lectins in epidemiologic investigations:

Basic affinity of lectins is due to their ability to bind to a variety of microbial substances, which are present on the cell surface carbohydrates. Schalla et al. in 1985 showed that lectins can be used for the epidemiological characterization of  Neisseria More Details gonorrhoea. [30] Rice et al. in 1986, observed that Gonococci failed to agglutinate with wheat germ lectin, a phenotypic marker for strain virulence. This lack of agglutination may represent alterations in the Gonococcal cell surface components, that is, decreased binding affinity of the cell surface carbohydrates of gonococci. [31]


  Conclusion Top


The role of lectins in research has been steadily increasing. This could be because of their general ability to bind with specific glycoconjugates. Lectins of plant and animal origin have been used effectively with various microorganisms to correlate virulence with their surface properties. Lectins have the capability for identification of the various strains of microorganisms and other infectious agents. The usefulness of lectins in clinical microbiology can be demonstrated by using empirical testing procedures. Lectin binding on the cell membranes has been shown to be associated with their high affinity to bind with such cell surface receptors, which can be an effective marker for assessing the progression of tumors. Lectins are unique and naturally occurring cytochemical and histochemical tools, which may further emphasize their values as potential diagnostic reagents for the clinical microbiologist.

 
  References Top

1.Komath SS, Kavitha M, Swamy MJ. Beyond carbohydrate binding: new directions in plant lectin research. Org Biomol Chem 2006;4:973-88.  Back to cited text no. 1
    
2.Rini JM. Lectin structure. Annu Rev Biophys Biomol Structure 1995;24:551-77.  Back to cited text no. 2
    
3.Rocca JD. Lectins as Next Generation Mucoadhesives for specific targeting of the gastrointestinal tract. Gastrointest Target Drug Develop 2004;4:12-9.  Back to cited text no. 3
    
4.Goldstein IJ, Hughes RC, Monsigny M, Osawa T, Sharon N. What should be called a lectin? Nature 1980;285:66.  Back to cited text no. 4
    
5.Vakri A, Cummings RD, Esko JD, Etzler ME, Surolia A, Cummings RD. Essential of glycobiology. Chapter 29 L- type lectins. 2 nd ed. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 2009: p. 341-5.  Back to cited text no. 5
    
6.Timothy Richard Helliwell. Lectin methods and protocols. Methods Mol Med 1997;9:73-94.  Back to cited text no. 6
    
7.AAllen, Brilliantine. A Survey of Hemagglutinins in Various Seeds. J Immun. 1969;102:1295-9.  Back to cited text no. 7
    
8.Gold ER and Balding P. Receptor-Specific Proteins: Plant and Animal Lectins. New York: Amer Elsevier. Pub; 1975, p. 120-389.  Back to cited text no. 8
    
9.Issitt PD. Applied Blood Group Serology. West Chester, Pa: Biological Corp of America; 1981. p. 77-9, p. 193.  Back to cited text no. 9
    
10.Kilpatrick DC, Graham C, Urbaniak SJ, Jeffree CE, Allen AK. A compartion of tomato (Lycopersicon esculentum) lectin with its deglycosylated derivative. Biochem J 1984;220:843-7.  Back to cited text no. 10
    
11.Nicolson GL, Blaustein J, Etzler ME. Characterization of two plant lectins from Ricinus communis and their quantitative interaction with a murine lymphoma. Biochemistry 1974;13:196-204.  Back to cited text no. 11
    
12.Damjanov I. Biologoical diseases. Lectin cytochemistry. Lab Invest 1987;57:5-20.  Back to cited text no. 12
    
13.Slifkin M, Doyle RJ. Lectins and their application to clinical microbiology. Clin Microbiol Rev 1990;3:197-218.  Back to cited text no. 13
    
14.Mirelman D, Galon E, Sharon N, Lotan R. Inhibition of fungal growth by wheat germ agglutinin. Nature (London) 1975;236:414-7.  Back to cited text no. 14
    
15.Lalwani AK, Carey TE, Goldstein IJ, Peters BP. Lectin binding charecteristics of squamous cell carcinomas of the head and neck. Acta otolaryngol 1996;116:125-31.  Back to cited text no. 15
    
16.Maruyama M, Onodera K, Ooya K. A histopathological and lectin - histochemical study of the lining epithelium in postoperative maxillary cysts. Oral Dis 2002;8:241-8.  Back to cited text no. 16
    
17.Bryne M, Reibel J, Mandel U, Dabelsteen E. Expression of mucin type carbohudrates may supplement histological diagnosis in oral premalignant lesions. J Oral Pathol Med 1991;20:120-5.  Back to cited text no. 17
    
18.Pillai KR, Remani P, Kannan S, Sujathan K, Mathew B, Vijayakumar T et al. Lectin histochemistry of oral premalignant and malignant lesions: Correlation of JFL and PNA binding pattern with tumor progression. Eur J Cancer B Oral Oncol 1996;32:32-7.  Back to cited text no. 18
    
19.Nachbar MS, Oppenheim DJ, Thomas JD. Lectins in the U.S diet isolation and characterization of a lectins from the tomato (Lycopersicon esculentum). J Biol Chem 1980;225:2056-61.  Back to cited text no. 19
    
20.Etaler ME. Distribution and function of plant lectins. In: Liener IE,Sharon N, Gold stein IJ, editor. The lectins, properties, functions and applications in biology and medicine. Orlando, Fla: Academic Press, Inc;1978. p 371-435.  Back to cited text no. 20
    
21.Mirelman D. Microbial lectins and agglutinins properties and biological activity. Newyork: John Wiley and Sons, Inc; 1986.  Back to cited text no. 21
    
22.Mirelman D, Altmann G, Eshdat Y. Screening of bacterial isolates for mannose specific lectin activity by agglutination of yeasts. J Clin Microbiol 1980;11:328-31.   Back to cited text no. 22
    
23.Slifkin M, Cumbie R. Identification of group B streptococcal antigen with lectin bound polystyrene particles. J Clin Microbiol 1987;25:1172-5.   Back to cited text no. 23
    
24.Sumner JB, Howell SF. The identification of the hemagglutinin of the jack bean with Concanavalin A. J Bacterial 1936;32:227-37.  Back to cited text no. 24
    
25.Barkai - Golan R, Sharon N . Lactins as a toll for the study of yeast cell wall. Exp Myol 1978;2:110-3.   Back to cited text no. 25
    
26.Ebisu S, Lonngren J, Goldstein IJ. Interaction of pneumococcal S -14 polysaccharide with lectins from Ricinous communis, Triticum Vulgaris and Bandeirarea simplicifolia. Carbohydr Res 1977;58:187-91.  Back to cited text no. 26
    
27.Galun M, Malki D, Galun E. Visualization of chitin wall formation in hyphae tips and anastomases of Diplodia natalensis by fluroscein - conjugated wheat agglutinin and [3H] N - acetyl D- glucosamine. Arch Microbiol 1981;130:105-10.  Back to cited text no. 27
    
28.Mirelman D, Galon E, Sharon N, Lotan R. Inhibition of fungal growth by wheat germ agglutinin. Nature (London) 1975;236:414-7.  Back to cited text no. 28
    
29.Tkacz JS, Cybolska EB, Lampson JO. Specific staining of wall mannan in yeast cells with fluorescein - conjugated Concanavalin A. J Bacteriol 1971;105:1-5.  Back to cited text no. 29
    
30.Schaller WD, Rice RJ, Biddle JW, Jean Louis Y, Larsen SA, Whitting ton WL. Lectin characterization of gonococci from an outbreak caused by penicillin - resistant Neisseria gonorrhoeae. J Clin Microbiol 1985;22:482-3.   Back to cited text no. 30
    
31.Rice RJ, Schalla WO, Whittington WL, JeanLouis Y, Biddle JW, Goldberg M, et al. Whittington. Phenotypic characterization of Neisseria gonorrhoea isolated from three cases meningitis. J Infect Dis 1986;153:362-5.  Back to cited text no. 31
    



 
 
    Tables

  [Table 1], [Table 2]


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