About the Lectin
Crude extracts of Vicia graminea seeds contain an agglutinin that is blood group N specific. The lectin exhibits a complex carbohydrate specificity. It is not inhibited by any mono- or disaccharides, although the O-linked blood group N antigen is a disaccharide with the structure Gal β(1,3)GalNAc. This carbohydrate structure is also recognized by the peanut lectin, but PNA binds to other galactose containing glycoconjugates as well. The peptide portion of the blood group N antigen is critical for binding of VGA. The extended binding site of the lectin reacts with clusters of O-linked Gal β(1,3)GalNAc adjacent to an N-terminal leucine residue 1,2 . Disaccharide clusters located on the first eight amino acids of O-linked glycopeptides react more strongly than these same clusters located on other amino acid residues 2 . VGA will bind to glycoproteins containing sialic acid, but removal of terminal sialic acid residues from these glycoproteins increases the reactivity of VGA. Both VGA and PNA can be used to probe the subtle differences in carbohydrate structure of various O-linked glycoconjugates. Both lectins recognize the same general structure; however, PNA will not react in the presence of a terminal sialic acid, while VGA will. VGA reacts only with a specific arrangement of clustered carbohydrates, while PNA does not require this arrangement. Crude VGA has been used to evaluate polyagglutinable erythrocytes from an individual with a hemoglobin variant called Hb M-Hyde Park 3 . VGA and the closely-realated Vicia unijuga agglutinin react specifically with certain small, perchloric acid-soluble glycoproteins called Vgu glycoproteins. These are associated with human malignant tumors 4,5 , but also occur in human amniotic fluid 6 and meconium 7 . Despite the presence of the N disaccharide, they do not react with anti-N serum 5,6 . Thus, VGA is an exceptionally useful reagent for detection of the Vgu glycoproteins. VGA has been purified using a combination of ion-exchange chromatography and gel filtration 8 , as well as by affinity chromatography on immobilized erythrocyte glycoproteins 9 . In all cases the lectin appears to be a tetramer composed of a single subunit. Isoelectric focusing gives multiple bands 10 , indicating that there is some heterogeneity of the subunits. Although VGA does not require additional ions for activity, it is a metalloprotein which is inactivated in the presence of EDTA. VGA is only available in crude form, but EY Laboratories can prepare the purified material on request. Contact the technical services department for information.
- Prigent, M. J., et al. (1984) Carbohydrate Res. 131 : 83-92.
- Duk, M., et al. (1982) Eur. J. Biochem. 123 : 105-112.
- King, M. J., et al. (1988) Transfusion. 28 : 549-555.
- Ueno, E., et al. (1992) Int. J. Biochem. 24 : 769-776.
- Ohyama, K., et al. (1997) Cancer Detect. Prev. 21 : 304-311.
- Ohyama, K., et al. (1997) Int. J. Biochem. Cell. Biol. 29 : 455-464.
- Uchide, N., et al. (1995) Int. Biochem. Cell Biol. 27 : 319-327.
- Prigent, M. J. and Bourrillon, R. (1976) Biochim. Biophys. Acta. 420 : 112-121.
- Lisowska, E., et al. (1976) FEBS Lett. 72 : 327-330.
- Duk, M. and Lisowska, E. (1981) Eur. J. Biochem. 118 : 131-136.
|Buffer||0.02M Phosphate – 0.1M NaCl, pH 6.5.|
|Activity||Less than 30 μl crude lectin/ml of buffer will agglutinate type N erythrocytes.|
|Inhibitory Carbohydrate||Not inhibited by simple sugars. Reacts with clusters of O-linked Galβ(1,3) GalNAc.|
Aggregate MW=120,000 Da. Each subunit has a molecular weight of 31,000 Da as determined by SDS-PAGE. Isoelectric focusing of the purified lectin gives multiple bands with a pI of 4.8-5.5.
EY Laboratories only offers the crude lectin. The informatioin concerning molecular weight and isoelecric point has been obtained by other researchers and has not been independently confirmed by EY Laboratories.