The purification, composition, and specificity of the anti-T lectin from peanut (Arachis hypogaea)

Peanut agglutinin was purified by affinity chromatography on Sepharose-epsilon-aminocaproyl-beta-D-galactopyranosylamine. The purified lectin obtained in a yield of 150 mg/100 g of defatted peanut was homogeneous on polyacrylamide gel electrophoresis, ultracentrifugation, and gel filtration. This intrinsic sedimentation coefficient (So20,w) and the intrinsic diffusion coefficient (Do20,w) were estimated at pH 7.4 as 5.7 +/- 0.1 S and 5.0 X 10(-7) cm2s(-1), respectively. The molecular weight of the agglutinin, determined by sedimentation and diffusion and by gel filtration, was found to be 110,000. Disc gel electrophoresis and gel filtration, both in the presence of sodium dodecyl sulfate, gave a single component of Mr = 27,500 suggesting that the lectin is a tetramer composed of four subunits. Four alanine residues per 110,000 g were found by NH2-terminal analysis and the sequence of the five NH2-terminal amino acids was: ALa-Glu-Ser-Val-Thr. Each cycle in a sequenator gave a single amino acid, suggesting that the four subunits are identical. Peanut agglutinin does not contain covalently bound sugar; it is devoid of cysteine and cystine, low in methionine, histidine, and tryptophan, but rich in acidic and hydroxyamino acids. The lectin agglutinated erthrocytes of human ABO blood types equally well, but only after they have been treated with neuraminidase. Of the monosaccharides tested for inhibition of hemagglutination only D-galactose and alpha- and beta-D-galactosides were active. High inhibitory activity was found with the Discaccharide DGalbeta(1 in equilibrium 3)DGalNAc and with the disialylated glycoproteins: alpha1-acid glycoprotein, fetuin, glycophorin, and human blood group NN or MM antigen. These desialylated glycoproteins also reacted with the lectin to form precipitin bands in Ouchterlony double diffusion in agar.