PURIFICATION AND CHARACTERIZATION OF A NEW MANNOSE-SPECIFIC LECTIN FROM STERNBERGIA-LUTEA BULBS

A new mannose-binding lectin was isolated from Sternbergia lutea bulbs by affinity chromatography on an alpha(1-2) mannobiose-Synsorb column and purified further by gel filtration. This lectin (S. lutea aggluti nin; SLA) appeared homogeneous by native-gel electrophoresis at pH 4.3 , gel filtration chromatography on a Sephadex G-75 column, and SDS-pol yacrylamide gel electrophoresis, These data indicate that SLA is a dim eric protein (20 kDa) composed of two identical subunits of 10 kDa whi ch are linked by non-covalent interactions. The carbohydrate binding s pecificity of the lectin was investigated by quantitative precipitatio n and hapten inhibition assays. It is an alpha-D-mannose-specific lect in that interacts to form precipitates with various alpha-mannans, gal actomannan and asialo-thyroglobulin, but not with alpha-glucans and th yroglobulin. Of the monosaccharides tested only D-mannose was a hapten inhibitor of the SLA-asialothryroglobulin precipitation system, where as D-glucose, D-galactose and L-arabinose were not. The lectin appears to be highly specific for terminal alpha(1-3)-mannooligosaccharides. The primary structure of SLA appears to be quite similar to that of th e snow drop (Galanthus nivalis) bulb lectin which is a mannose-binding lectin from the same plant family Amaryllidaceae. The N-terminal 46 a mino acid sequence SLA showed 76% homology with that of GNA.