The complete amino acid sequence of the α-subunit of pea lectin, Pisum sativum

The complete primary structure of the α-subunit of the lectin from the pea (Pisum sativum) has been determined using a combination of tryptic and staphylococcal protease digestion, purification using Sephadex gel filtration and high-voltage electrophoresis followed by either manual or automated Edman degradation. The molecular weight of the α-subunit from sequence data and gel filtration in guanidine-HCl is close to 5800, which is lower than that determined by sedimentation equilibrium techniques. The sequence reveals considerable homology to concanavalin A and near identity to the α-subunit of the lentil lectin (Lens culenaris). As in the case of the lentil α-subunit, the α-methyl glucose binding site(s) are not present in this region, nor are the S₁ and S₂ metal ion binding sites as judged by homology consideration, though the residues for the S₃ lanthanide binding (Glu 87 and Asp 136) are conserved from the available data on the α- and β-subunits. Preliminary metal exchange experiments on the intact pea lectin indicate some differences in the metal exchange properties of this lectin compared to concanavalin A, and therefore possible ligand variations in this region of the β-subunit.