PURIFICATION AND CHARACTERIZATION OF THE ALPHA-1,3-MANNOSYLMANNOSE-RECOGNIZING LECTIN OF CROCUS-VERNUS BULBS

A unique mannose-binding lectin, highly specific for terminal Man(alph a 1,3)Man groups, was isolated from bulbs of crocus (Crocus vernus All .), The lectin failed to bind to a mannose affinity column and was pur ified by simple gel permeation chromatography (Sephacryl S200). The pu rified lectin, obtained in crystalline form, had a molecular mass of 4 4 kDa on gel filtration and showed a single peptide band with a molecu lar mass of 11 kDa on SDS-polyacrylamide gel electrophoresis, indicati ng it to be a tetrameric protein composed of four identical subunits, The N-terminal amino acid sequence analysis of the crocus lectin showe d essentially no homology with that of other mannose-binding bulb lect ins. The crocus lectin selectively interacted with the wild type Sacch aromyces cerevisiae and other mannans carrying terminal Man(alpha 1,3) Man but not with those lacking this disaccharide unit, In hapten inhib ition studies, methyl alpha-mannopyranoside did not inhibit the mannan -lectin interaction, Of various alpha-mannooligosaccharides, those hav ing the Man(alpha 1,3)Man sequence showed the highest inhibitory poten cy, confirming the strict requirement of lectin for terminal alpha 1,3 -linked mannosylmannose units, An affinity column of immobilized lecti n enabled the complete resolution of yeast mannan and glycogen, The im mobilized lectin may provide a useful tool for purification and analys is of biologically important polysaccharides and glycoproteins.