Purification of potato lectin (Solanum tuberosum agglutinin) from tubers or fruits using chromatofocusing

Utility of pentose colorimetric assay for the purification of potato lectin, an arabinose-rich glycoprotein

Potato lectin (Solanum tuberosum agglutinin, STA) is an unusual glycoprotein containing approximately 50% carbohydrates by weight. Of the total carbohydrates, 92% is contributed by L: -arabinose, which are O-linked to hydroxyproline residues. The ferric chloride-orcinol assay (Bial's test), which is specific for pentoses has so far been used only for the determination of free pentoses in biological samples. However, this colorimetric assay has not been used for the detection of pentoses in bound form as it occurs in Solanaceae lectins (potato, tomato, and Datura lectins). Utilizing the pentose colorimetric assay for monitoring the presence of potato lectin, a simpler and shorter procedure for the purification of this lectin from potato tubers has been developed. The yield of potato lectin (1.73 mg per 100 g potato tuber) is twice compared to the yields reported in earlier procedures. Although potato lectin is well known for its specificity to free trimers and tetramers of N-acetyl-D: -glucosamine (GlcNAc), it possesses a similar specificity to the core (GlcNAc)(2) of N-linked glycoproteins. The utilization of the pentose assay in the purification of arabinose-rich lectins/agglutinins obviates the necessity for the use of agglutination assay in the various purification steps. The pentose assay appears to be a simple and convenient colorimetric assay for detecting any pentose-rich glycoprotein in plant extracts. The utility of the pentose assay appears to have a significant potential in the detection of hydroxyproline-rich glycoproteins (HRGPs), which are generally O-arabinosylated.

Datura lectin is both an anti-mitogen and a co-mitogen acting synergistically with phorbol ester

The lectins from Datura stramonium, Lycopersicon esculentum, and Solanum tuberosum are structurally related and possess a similar carbohydrate specificity, yet the Datura lectin is mitogenic for human lymphocytes while the other two are not. However, the Datura lectin was found to antagonize blast transformation induced by purified protein derivative (PPD), even within the concentration range at which it was optimally mitogenic on its own. The presence of a submitogenic concentration of the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) enormously enhanced the mitogenic activity of Datura lectin. No such synergy was observed, however, between tomato lectin or S. tuberosum agglutinin (STA) and TPA, nor between Datura lectin and the calcium ionophore A 23187.