Structural comparison of the lectin from sainfoin (Onobrychis viciifolia) with concanavalin A and other D-mannose specific lectins

The D-mannose specific lectin from sainfoin was prepared by affinity chromatography on Sephadex G-75, and its circular dichroism (CD), metal content, antigenic character, and N-terminal amino acid sequence were compared with those of four lectins from Vicieae plants and concanavalin A. The sainfoin lectin was only slightly more closely related to these other D-mannose specific lectins, than to lectins of leguminous plants in general. The CD and antigenic experiments also confirmed the close relationship of the four Vicieae lectins. The N-terminal sequence showed sainfoin has two isolectins, differing in sequence at residue four. The sequence was homologous to N-terminal sequences of several other lectins; hence, despite some structural and specificity similarities, the sainfoin lectin does not show the circular permutation of sequence unique to concanavalin A. This region also contained the sole cysteine residue, at position 33. The carbohydrate-binding properties of the sainfoin lectin were studied by gradient affinity chromatography. Its apparent Ka for methyl alpha-D-glucoside was approximately 10(3) M-1, close to the Ka of the pea lectin. However, in the relative binding behaviour of methyl alpha-D-mannoside, maltose, and methyl alpha-D-glucoside, it resembled concanavalin A more than the pea lectin.