C-TERMINAL POSTTRANSLATIONAL PROTEOLYSIS OF PLANT-LECTINS AND THEIR RECOMBINANT FORMS EXPRESSED IN ESCHERICHIA-COLI - CHARACTERIZATION OF RAGGED ENDS BY MASS-SPECTROMETRY

Electrospray mass spectrometry was used to accurately measure the mole cular masses of single chain lectins from legume seeds and also of thr ee recombinant lectins, expressed in Escherichia coli, The five single chain lectins, Erythrina corallodendron lectin, soybean and peanut ag glutinins, Dolichos biflorus lectin, and Phaseolus vulgaris hemaggluti nin E, all showed evidence of C-terminal proteolytic processing, in so me cases to ''ragged'' ends, when their masses were compared to those expected from their cDNA sequences and their known carbohydrate chains . Recombinant forms of the lectins from E, corallodendron, soybean, an d peanut also showed C-terminal trimming, but not to the same points a s the natural forms, Discrepancies between the protein and cDNA sequen ces of the E. corallodendron lectin were resolved by combined liquid c hromatography-mass spectrometry peptide mapping and protein sequencing experiments, and the presence of a second glycosylation site was demo nstrated, Our data show that all of these lectins undergo C-terminal p roteolytic processing of a readily attacked peptide segment, This trim ming is frequently imprecise, and the resulting heterogeneity may be a major contributor to the appearance of isolectin forms of these prote ins.