The alpha-mannosyl-binding lectin from leaves of the orchid twayblade (Listera ovata). Application to separation of alpha-D-mannans from alpha-D-glucans.

The carbohydrate-binding specificity of an alpha-D-mannose-specific lectin isolated from leaves of the orchid twayblade (Listera ovata) was elucidated by quantitative precipitation of mannose-containing polysaccharides and glycoproteins, hapten inhibition, and affinity chromatography on the immobilized lectin. L. ovata agglutinin (LOA) interacted with various alpha-mannans and galactomannans of yeasts, fungi and bacteria, but not with alpha-glucans, e.g., dextran and glycogen, as do mannose/glucose-binding lectins. This lectin, LOA, appears to be highly specific for alpha 1-3 mannosidic linkages. It reacted with a linear alpha 1-3-mannan (D. P. 15) and, surprisingly, even with a linear alpha 1-3-mannoheptasaccharide. The LOA/C. tropicalis mannan precipitation reaction was inhibited by alpha-linked mannooligosaccharides, in the order, alpha 1-3 > alpha 1-6 > alpha 1-2 linkages; alpha 1-3 [Man]4 and [Man]5 were the best inhibitors among various mannooligosaccharides tested, having 7-times greater potency than alpha 1-3 [Man]2, and 18-times that of methyl, alpha-mannoside. LOA/mannan interaction was also inhibited by periodate-oxidized and reduced alpha 1-3 [Man]5 which had an inhibitory potency similar to that of alpha 1-3 [Man]3, confirming that LOA also recognizes the internal alpha 1-3-mannosidic linkages of carbohydrate chains. Complete resolution of mannan and glycogen from yeast cells, by affinity chromatography on an immobilized LOA column, and retention of several high-mannose-glycoproteins suggest this lectin to be a useful tool for purification and structural investigation of alpha-mannosyl-containing polysaccharides and glycoconjugates.