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

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Abstract
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 4 lectins from Vicieae plants [Pisum sativum, Lens culinaris, Vicia faba and Lathyrus odoratus] 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 4 Vicieae lectins. The N-terminal sequence that sainfoin has 2 isolectins, differing in sequence at residue 4. The sequence weas homologous to N-terminal sequences of several other lectins; so, despite some structural and specificity similarities, the sainfoin lectin does not have 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 .apprx. 103 M-1, close to the Ka of the pea lectin. In the relative binding behavior of methyl .alpha.-D-mannoside, maltose and methyl .alpha.-D-glucoside, it resembled concanavalin A more than the pea lectin.