Purification and characterization of Dolichos lablab lectin

The mannose/glucose-binding Dolichos lablab lectin (designated DLL) has bee n purified from seeds of Dolichos lablab (hyacinth bean) to electrophoretic homogeneity by affinity chromatography on an ovalbumin-Sepharose 4B column . The purified lectin gave a single symmetric protein peak with an apparent molecular mass of 67 kDa on gel filtration chromatography, and five bands ranging from 10 kDa to 22 kDa upon SDS-PAGE, N-Terminal sequence analysis o f these bands revealed subunit heterogeneity due to posttranslational prote olytic truncation at different sites mostly at the carboxyl terminus. The c arbohydrate binding properties of the purified lectin were investigated by three different approaches: hemagglutination inhibition assay, quantitative precipitation inhibition assay, and ELISA, On the basis of these studies, it is concluded that the Dolichos lablab lectin has neither an extended car bohydrate combining site, nor a hydrophobic binding site adjacent to it. Th e carbohydrate combining site of DLL appears to most effectively accommodat e a nonreducing terminal alpha-D-mannosyl unit, and to be complementary to the C-3, C-4, and C-6 equatorial hydroxyl groups of alpha-D-mannopyranosyl and alpha-D-glucopyranosyl residues. DLL strongly precipitates murine IgM b ut not IgC, and the recent finding that this lectin interacts specifically with NIH 3T3 fibroblasts transfected with the Flt3 tyrosine kinase receptor and preserves human cord blood stem cells and progenitors in a quiescent s tate for prolonged periods in culture, make this lectin a valuable tool in biomedical research.