Isolation and Partial Characterization of Two Plant Lectins 1S.N
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Current Research Journal of Biological Sciences 2(4): 232-237, 2010 ISSN: 2041-0778 © Maxwell Scientific Organization, 2010 Submitted Date: March 30, 2010 Accepted Date: April 13, 2010 Published Date: July 20, 2010 Isolation and Partial Characterization of Two Plant Lectins 1S.N. Laija, 2S. Mahesh, 1L.S. Smitha and 1P. Remani 1Laboratory of Glycobiology and Phytopharmacology, Division of Cancer Research, Regional Cancer Centre, Thiruvananthapuram, Kerala, India 2Department of Botany, Christian College, Thiruvananthapuram, Kerala, India Abstract: Plant lectins with different sugar specificities were isolated from the seeds of Artocarpus integrifolia and Canavalia gladiata using a procedure that involved affinity chromatography. Of the two lectins isolated, protein content was found to be more in Artocarpus integrifolia than in Canavalia gladiata whereas carbohydrate content was more in Canavalia gladiata. Both the lectins were found to be stable up to 100ºC. Lectin from Artocarpus integrifolia showed two bands with molecular weight 11 and 17 kDa. Canavalia gladiata also gave two dissimilar bands of molecular weight 26 and 17 kDa both in the presence and absence of $-mercaptoethanol. Carbohydrate staining of SDS gel indicated that both the bands are glycosylated Canavalia gladiata whereas only one band was glycosylated in Artocarpus integrifolia. Key words: Artocarpus integrifolia, Canavalia gladiata, lectin, mannose, N-acetyl galactosamine INTRODUCTION In recent years, lectins have become very attractive due to their extensive use as probes for both the Plants are the richest and most convenient source of characterization and isolation of simple and complex lectins. Plant lectin has been attracting much attention sugars (Rudiger and Gabius, 2001; Sharon and Lis, 2002) because of their ease of isolation and their usefulness as and as useful tools in immunological studies reagents for glycoconjugates in solution and on cell (Moreira et al., 1991). Considering the innumerable surface. Lectins were discovered by their ability to number of lectins available in the nature, the ease with agglutinate erythrocytes and probably the easiest and most which they could be prepared in the purified form, their convenient method of detecting lectin activity remains amenability to chemical manipulation and the fact that agglutination of a panel of human and/or animal red blood they can be inhibited by simple sugars makes them cells or other cells. Lectins are particularly prevalent in attractive as an important tool in biological research. leguminous plants, where they are localized in the Although lectins are found ubiquitously in plant species, cotyledons of the seeds and roots. Lectins may comprise they have variable structures and specific activities up to 3% of the weight of a mature seed. according to the plants they originate from. Thus Lectins have precise carbohydrate specificity and can purification and characterization of lectins from a variety be blocked by simple sugars and oligosaccharides. of plant species interests researchers in the field of Because of the specificity each lectin has towards a glycobiology. This study reports the purification and particular carbohydrate structure, even oligosaccharides characterization of lectin from Canavalia gladiata and with identical sugar composition can be distinguished or Artocarpus integrifolia. separated. The actual structure recognized by the binding site of the lectin when it combines with its natural ligand MATERIALS AND METHODS is generally large and more complex than a single monosaccharide. Lectins, which have a similar specificity Seeds of Canavalia gladiata and Artocarpus towards monosaccharides, may differ in their affinity for integrifolia were collected locally and used for the a particular disaccharide, oligosaccharide or glycopeptide. isolation of lectin. The present study was conducted at Lectins vary in composition, molecular weight, Regional Cancer Centre, Kerala. subunit structure and number of sugar binding sites per molecule. By virtue of the abundance of lectins in Haemagglutination assay: The haemagglutination assay legumes, most of the reports are confined to the was carried out using the method described by biochemical analysis of lectins in the different members Pueppke (1979). Human erythrocytes of A, B and O of the legume family. Only a few have been studied for phenotypes were used. The assays were carried out in their biological application. WHO plates with a final volume of 400 :L in each well. Corresponding Author: Laija S. Nair, Department of Botany, Government Sanskrit College, Pattambi- 679306, Palakkad, Kerala, India 232 Curr. Res. J. Biol. Sci., 2(4): 232-237, 2010 Decreasing concentration of the seed extracts was taken pH became neutral. It was transferred to 20 mL of in the wells by two fold serial dilution with PBS to PBS (pH 7.4) and was then homogenized in a blender to determine the agglutination titre. PBS was added in the the correct particle size (about 300 mm). It was again control wells instead of plant extract. Washed washed in PBS (pH 7.4) several times. The homogenized erythrocytes were added at a concentration of 2% in PBS guar gum was then packed to a height of 30 cm in a 2.5 and incubated at room temperature for 2 h. The minimum cm diameter glass column equipped with flow adapter and concentration of the extract that gave haemagglutination equilibrated with PBS (pH 7.4). was recorded as the haemagglutination titre. The column kept at 4°C was run at a rate of 100 mL/h, first with PBS until the absorbency of the effluent Neuraminidase treatment of erythrocytes: at 280nm became equal to that of PBS. The isolated lectin Neuraminidase treated erythrocytes were used for seed solution was then applied to the top of the column. The extracts which were found negative in direct column was then washed extensively with PBS until the haemagglutination assay. Packed human erythrocytes absorbance of the effluent at 280 nm became equal to or (0.5 mL) were washed in PBS (pH 7.4) three times and less than 0.05. The absorbed lectin was then eluted using suspended in 2 mL of acetate buffered saline (pH 5.6). It a solution of N-acetyl D-galactosamine (20 mM in PBS). was incubated for 30 min at 30°C with 20 :L of Vibrio The effluents were collected in 2 mL aliquots and the cholerae neuraminidase. The cells were then washed two absorbance of each fraction was read at 280nm. The times in PBS and were then resuspended in PBS to make fractions with maximum absorbance were pooled and 2% w/v solution. dialyzed against several changes of distilled water. The dialyzed jackfruit lectin was then lyophilized and kept in Isolation and purification of Artocarpus integrifolia the dessicator. lectin: Ripened seeds from Artocarpus integrifolia were collected. Twenty five gram of the seeds were deskinned Isolation and purification of Canavalia gladiata lectin: and ground to flour. The flour was defatted by soaking in Defatted, finely ground seeds of Canavalia gladiata, 50 petroleum ether for 24 h at room temperature. The g, were suspended in 0.15M NaCl and stirred overnight in defatted flour was stirred well on a magnetic stirrer with the cold. The resulting suspension was and the residue 250 mL of phosphate buffered saline overnight at 4°C. discarded. The filtrate was then centrifuged for one hour The extract was filtered and spun for 30 min at 10,000 g. at 10000 rpm and the residue discarded. The supernatant The supernatant was collected and ammonium sulphate solution was made 30% saturated with ammonium was added to the sample with constant stirring to a sulphate by gradual addition of the solid salt. The mixture concentration of 40% saturation and kept overnight. The was stirred at room temperature for four hours and the precipitates were removed by centrifugation at 20,000 g precipitated proteins were removed by centrifugation at for 30 min. The clear supernatant was then adjusted to 10000 rpm for one hour and discarded. The protein was 60% saturation by further addition of ammonium sulphate then precipitated by adding ammonium sulphate to 80% with constant stirring and kept overnight. The precipitate saturation. The precipitate was collected by centrifugation thus formed was collected by centrifugation as above, as above, dissolved in distilled water and dialyzed in cold dissolved in 20ml of PBS and then dialyzed extensively against several changes of distilled water, and finally against three changes of PBS (pH 7.2). Any precipitate against 1.0M NaCl. formed was removed by centrifugation and the clear The isolated Canavalia gladiata lectin was then supernatant was collected. The isolated lectin was then purified by the adsorption of lectin to sephadex G-75. A purified by affinity chromatography on cross-linked guar column of sephadex G-75 was prepared and equilibrated gum columns. with 1.0 M NaCl and the flow rate was adjusted to Soluble guar gum was purchased from Sigma 30-40 mL/h. The protein solution from above, in 1M Chemical Company. Insoluble guar gum was prepared by NaCl, was applied to the column, which was connected to cross-linking the soluble polysaccharide using a reservoir of 1M NaCl. Fractions were collected every 15 epichlorohydrin. A fine emulsion of 1.5 mL of min and monitored for protein by absorbance at 280nm. epichlorohydrin in 25 mL of 3N Sodium hydroxide was After the absorbance at 280 nm#0, 1 M solution of prepared in a 100 mL-stoppered bottle by thorough glucose in 1 M NaCl was added to elute the lectin from mixing. The emulsion was then poured into 250 mL the dextran gel. The effluents were collected in 2ml beaker followed by 10 g of guar gum powder, stirring the aliquots and the absorbance of each fraction was read at mixture vigorously until it solidified and kept at 40°C in 280 nm. The fractions with maximum absorbance were water bath for 24 h with occasional stirring. Then it was pooled and dialyzed to remove glucose and concentrated.