The mannose-specific lectins from ramsons (Allium ursinum L.) are encoded by three sets of genes

Abstract

Lectin cDNA clones encoding the two mannose-binding lectins from ramsons (allium ursinum L.) bulbs, AUAI and AUAII (AUA, Allium ursinum agglutinin), were isolated and characterized. Sequence comparison of the different cDNA clones isolated revealed three types of lectin clones called LECAUAG0, LECAUAG1 and LECAUAG2, which besides the obvious differences in their sequences also differ from each other in the number of potential glycosylation sites within the C-terminal peptide of the lectin precursor. In vivo biosynthesis studies of the ramson lectins have shown that glycosylated lectin precursors occur in the organelle fraction of radioactively labeled ramson bulbs. Despite the similarities between the A. ursinum and the A. sativum (garlic) lectins at the protein level, molecular cloning of the two ramson lectins has shown that the lectin genes in A. ursinum are organized differently. Whereas in A. sativum the lectin polypeptides of the heterodimeric ASAI are encoded by one large precursor, those of the heterodimeric AUAI lectin are derived from two different precursors. These results are confirmed by Northern blot hybridization of A. ursinum RNA which, after hybridization with a labeled lectin cDNA, reveals only one band of 800 nucleotides in contrast to A. sativum RNA which yields two bands of 1400 and 800 nucleotides. Furthermore it is shown that the two mannose-binding lectins are differentially expressed.