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

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)-alpha-D-mannan and S. cerevisiae mannan, weakly with a synthetic (1----6)-alpha-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 linear mannans, suggesting that the two lectins have somewhat different binding specificities for alpha-D-mannosyl units. Of the saccharides tested as inhibitors of precipitation, those with alpha-(1----3)-linked mannosyl units were the best inhibitors of ASA, the alpha-(1----2)-, alpha-(1----4)-, and alpha-(1----6)-linked mannobioses and biosides having less than one eighth the affinity of the alpha-(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 alpha-D-mannosyl-binding lectin.