POSTTRANSLATIONAL PROTEOLYTIC PROCESSING AND THE ISOLECTINS OF LENTILAND OTHER VICIAE SEED LECTINS

Electrospray mass spectrometry was used to identify precisely the prot eolytic cleavage points within, and at the C-termini of, the proprotei n forms of four Viciae lectins that give rise to their two-chain forms . The lectins examined were the pea and lentil lectins, favin and the Lathyrus odoratus lectin, which represent each of the four genera in t his tribe. The molecular mass data showed single beta-chain forms for each lectin, with masses consistent with the available sequence and gl ycopeptide data, indicating that each came from a single proprotein. I n contrast, the pea, lentil and L. odoratus alpha-chains occurred in a s many as five forms, due to multiple C-terminal cleavage points. Only favin showed a single alpha-chain form. The alpha-chain mass data wer e again consistent with the sequence information available, except for the lentil lectin alpha-chain which was re-determined by protein sequ encing. The two isolectin forms of this protein were shown to arise fr om alpha-chain species with and without residue Lys53. The mass spectr um of concanavalin A was also examined and both the single-chain form and the two fragment forms showed no evidence of C-terminal heterogene ity.