J Biol Chem, Vol. 274, Issue 47, 33300-33305, November 19, 1999

Xanthosoma sagittifolium Tubers Contain a Lectin with Two Different Types of Carbohydrate-binding Sites

Hanqing Mo, Kevin G. Rice^§, David L. Evers^§, Harry C. Winter, Willy J. Peumans^¶, Els J. M. Van Damme^¶, and Irwin J. Goldstein

From the  Department of Biological Chemistry, University of Michigan, Medical School, Ann Arbor, Michigan 48109-0606, the ^§ Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, and the ^¶ Laboratorium voor Fytopathologie en Plantenbescherming, Katholieke Universiteit Leuven, Willem de Croylaan 42, B-3001 Leuven (Heverlee), Belgium

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-Sepharose and invertase-Sepharose. SDS-polyacrylamide gel electrophoresis, N-terminal amino acid sequencing, and gel filtration chromatography of the purified lectin showed that the X. sagittifolium lectin is a heterotetrameric protein composed of four 12-kDa subunits (₂₂) linked by noncovalent bonds. The results obtained by quantitative precipitation and hapten inhibition assays revealed that the lectin has two different types of carbohydrate-combining sites: one type for oligomannoses, which preferentially binds to a cluster of nonreducing terminal 1,3-linked mannosyl residues, and the other type for complex N-linked carbohydrates, which best accommodates a non-sialylated, triantennary oligosaccharide with N-acetyllactosamine (i.e. Gal1,4GlcNAc-) or lacto-N-biose (i.e. Gal1,3GlcNAc-) groups at its three nonreducing termini.