A novel mannose-specific and sugar specifically aggregatable lectin from the bark of the Japanese pagoda tree (Sophora japonica)

A new D-mannose/D-glucose-specific lectin (B-SJA-II) was isolated from the bark of the Japanese pagoda tree, Sophora japonica. B-SJA-II was separated from a well known D-galactose/N-acetyl-D-galactosamine-specific lectin (B-SJA-I) by affinity chromatography on lactamyl-Sepharose, then purified by affinity chromatography on maltamyl-Sepharose. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, B-SJA-II gave four bands: subunit a-1 (Mr = 19,400), a-2 (Mr = 18,200), b-1 (Mr = 15,000), and b-2 (Mr = 13,200). Carbohydrate analysis and binding study with horseradish peroxidase-labeled lectins on the bands electroblotted onto polyvinylidene difluoride membrane showed that the three subunits other than b-2 have N-linked oligosaccharides typical of plant glycoproteins. The binding assay with horseradish peroxidase-glycoproteins revealed that all the subunits can bind sugar specifically with fetuin and asialofetuin. Furthermore, B-SJA-II aggregated to form precipitates in the absence of a specific sugar and became soluble upon addition of the specific sugar. The results indicate that each subunit has a sugar-binding site for the mannosyl core of N-linked oligosaccharide chains and recognizes each other sugar specifically to form aggregates. According to the N-terminal amino acid sequences obtained, the subunits are classified into two groups. The first group (a-1 and a-2) has an N-terminal sequence 50% identical with that of other S. japonica lectins (Hankins, C. N., Kindinger, J. I., and Shannon, L. M. (1988) Plant Physiol. 86, 67-70) and the amino acid sequence initiating at position 123 of concanavalin A (Cunningham, B. (1975) J. Biol. Chem. 250, 1503-1512), while the N-terminal sequence of the second group (b-1 and b-2) is homologous to that of concanavalin A, but completely different from that of the first group.