About the Lectin
A lectin, from Amaranthus caudatus L. has been isolated and purified from its seed. This lectin, Amaranthin, is a homodimer (62 kDa) composed of lectin polypeptides of 33-36 kDa, which are not held together by disulphide bonds1,2. The protein is not glycosylated. Amaranthin readily forms a precipitate with glycoproteins and glycoconjugates containing Galβ(1,3) GalNAc a-units. Hapten inhibition of precipitate formation between amaranthin and a sialo-ovine submaxillary indicated that the T-antigen disacccharide and it’s a-linked glycosides (Galβ(1,3) GalNAc a-O-R; R=OH, methyl, -(CH2)8–COOH, allyl, o-nitrophenyl or benzyl) were the best inhibitors.
N-acetylgalactosamine, the only monosaccharide which inhibited precipitation was 350-fold less effective than Galβ(1,3) GalNAc a-O-R. Sequence analysis revealed that the protein is N-terminally blocked1. The amino acid composition of the lectin is typified by high concentrations of acidic and hydroxyamino acids and relatively large amounts of lysine, methionine and tryptophan for a plant protein1. Another report describes the purification of the Amaranthin by affinity chromatography on asialofetuin-linked amino activated silica3. In contrast to the report by Rinderle et al.2 Singh et al.3 claim that Amaranthus lectin is a glycoprotein containing 1.65 % carbohydrate.
The Amaranthus lectin (ACA) agglutinates human ABO and sheep, goat, rat, rabbit and guinea-pig erythrocytes3. ACA may be a highly specific tool probe for the T- and cryptic T-antigens1. ACA may be used with other lectins of close carbohydrate binding specificity to compliment the Galβ(1,3) GalNAc–linkage of the dissacharides. ACA is used as a histochemical probe for proliferating cells in sections of human colonic tissues4.
ACA represents about 3.7% of the PBS–extracted protein in seed meal1. This lectin is present in seeds only and not in stems or in leaves2. A lectin of similar T-antigen binding specificity is present in Artocarpus integrifolia seeds (AIA). In addition to ACA in the A. caudatus seeds, there are also two small chitin-binding proteins present. These proteins, called Ac-AMP1 and Ac-AMP2 have antimicrobial activity and show sequence similarity to hevein5.
- Rinderle, S.J. et al., J. of Biological Chemistry 264, (1989) 16123-16131.
- Rinderle, S.J. et al., Biochemistry 29 (1990) 10555-10561.
- Singh J., etal, Plant Science 94 (1993) 47-53.
- Boland, C. R., et al., Cancer Research 51, (1991) 657-665.
- Broekaert, W.F., et al., Biochemistry 31, (1992) 4308-4313.
|Buffer||0.01M Phosphate – 0.15M NaCl, pH 7.2-7.4.|
|Activity||ACA agglutinates human ABO and sheep, goat, rat, rabbit and guinea-pig erythrocytes3.|
|Inhibitory Carbohydrate||GalNAc (T-antigen disaccharide and its α-linked glycosides (GALβ (1,3) GalNAcα-O-R))|
|Molecular Weight||This lectin, Amaranthin, is a homodimer (62 kDa) composed of lectin polypeptides of 33-36 kDa, which are not held together by disulphide bonds1,2.|