MASS-SPECTROMETRIC ANALYSIS OF GENETIC AND POSTTRANSLATIONAL HETEROGENEITY IN THE LECTINS JACALIN AND MACLURA-POMIFERA AGGLUTININ

Jacalin and M. pomifera agglutinin are T-antigen specific lectins with alpha(4) beta(4) structures that show far greater microheterogeneity than plant lectins from other families, due to multiple genetic isofor ms and post-translational processing. Electrospray mass spectrometry a nd combined liquid chromatography-electrospray mass spectrometry were used to characterize the various forms. For both lectins, the mass dat a were consistent with previous protein sequencing of the major alpha- chain species of 133 residues and three beta-chain species of 20 or 21 residues. In addition, for jacalin the mass of one minor alpha-chain species was consistent with a second of the four reported gene sequenc es. However, the glycopeptide alpha-chain form and one beta-chain form did not match any of the genes, suggesting a fifth gene remains to be found. For M. pomifera agglutinin, three more beta-chain forms were f ound, but all six could arise from only two genes, with additional pos t-translational proteolysis and post-translational substitution with a n unidentified component of 106 Da creating the set of six forms. Only two alpha-chain forms were found also, with no glycosylation.