New mannose-specific lectins from garlic (Allium sativum) and ramsons (Allium ursinum) bulbs

Abstract Two new mannose-binding lectins were isolated from garlic ( Allium sativum , ASA) and ramsons ( Allium ursinum , AUA) bulbs, of the family Alliaceae, by affinity chromatography on immobilized mannose. The carbohydrate-binding specificity of these two lectins was studied by quantitative precipitation and hapten-inhibition assay. ASA reacted strongly with a synthetic linear (1 → 3)-α- d -mannan and S. cerevisia mannan, weakly with a synthetic (1 → 6)-α- d -mannan, and failed to precipitate with galactomannans from T. gropengiesseri and T. lactis-condensi , a linear mannopentaose, and murine IgM. On the other hand, AUA gave a strong reaction of precipitation with murine IgM, and good reactions with S. cerevisiae mannan and both synthetic mannans, suggesting that the two lectins have somewhat different binding specificities for α- d -mannosyl units. Of the saccharides tested as inhibitors of precipitation, those with α-(1 → 3)-linked mannosyl units were the best inhibitors of ASA, the α-(1 → 2)-, α-(1 → 4)-, and α-(1 → 6)-linked mannobioses and biosides having less than one eighth the affinity of the α-(1 → 3)-linked compounds. The N -terminal amino acid sequence of ASA exhibits 79% homology with that of AUA, and moderately high homology (53%) with that of snowdrop bulb lectin, also an α- d -mannosyl-binding lectin.