Xanthosoma sagittifolium tubers contain a lectin with two different types of carbohydrate-binding sites

An unusual lectin possessing two distinctly different types of carbohydrate combining sites was purified from tubers of Xanthosoma sagittifolium L. by consecutive passage through two affinity columns, i.e. asialofetuin-Sephar ose and invertase-Sepharose. SDS-polyacrylamide gel electrophoresis, N-term inal amino acid sequencing, and gel filtration chromatography of the purifi ed lectin showed that the X sagittifolium lectin is a heterotetrameric prot ein composed of four 12-kDa subunits (alpha(2)beta(2)) linked by noncovalen t bonds. The results obtained by quantitative precipitation and hapten inhi bition assays revealed that the lectin has two different types of carbohydr ate-combining sites: one type for oligomannoses, which preferentially binds to a cluster of nonreducing terminal alpha 1,3-linked mannosyl residues, a nd the other type for complex N-linked carbohydrates, which best accommodat es a non-sialylated, triantennary oligosaccharide with N-acetyllactosamine (i.e. Gal beta 1,4GlcNAc-) or lacto-N-biose (i.e. Gal beta 1,3GlcNAc-) grou ps at its three nonreducing termini.