Lectin from sainfoin (Onobrychis viciaefolia Scop.). Complete amino acid sequence

Abstract

The complete amino acid sequence of a lectin from sainfoin (O. viciifolia Scop. cv. Eski) was been determined by sequential Edman analyses of the intact protein and peptides derived from digests with trypsin and thermolysin. Peptides were purified by pH fractionation, by gel filtration and by cation-exchange and reverse-phase high-performance liquid chromatography. Seven segments of continuous sequence, accounting for the entire protein, were aligned through sequence comparison with several homologous leguminous lectins to give the final structure. Sainfoin lectin monomer, a glycoprotein which contains a single polypeptide chain of 236 amino acid residues with a MW of 26,509, has amino- and carboxyl-terminal residues of alanine and threonine, respectively. A single residue of cysteine, located at position 33, is the only S-containing amino acid present. Asparagine-118 is the single oligosaccharide attachment site. At least 2 apparent allelomorphic forms of the protein, having valine or isoleucine at position 49 in equal amounts, were detected. The amino acid sequence of sainfoin lectin exhibits circular permutation relative to that of the homologous protein concanavalin A.