Purification of a trypsin-stable lectin with antiproliferative and HIV-1 reverse transcriptase inhibitory activity

A lectin, with a molecular mass of approximately 60 kDa and two different subunits exhibiting an N-terminal sequence manifesting considerable homology to phytohemagglutinin from Phaseolus species, was isolated from the ground bean (Vigna sesquipedalis cv ground bean). The lectin was unique in hemagglutinating activity was inhibited by polygalacturonic acid and not by galacturonic acid and other simple monosaccharides. The lectin was isolated by affinity chromatography on Affi-gel blue gel, ion exchange chromatography by fast protein liquid chromatography (FPLC) on Mono S, and gel filtration by FPLC on Superdex 75. It was adsorbed on both Affi-gel blue gel and Mono S. Ground bean lectin exhibited mitogenic activity on murine splenocytes with the maximal response achieved at a concentration of 156 nM, as similar to the dose required for Con A. The viability of hepatoma (HepG2), leukemia (L1210), and leukemia (M1) cells was reduced in the presence of ground bean lectin, which also exerted an inhibitory activity toward HIV-1 reverse transcriptase IC(50) of 73 microM. The hemagglutinating activity of the lectin was unaffected by trypsinization and the presence of a number of divalent cations, but was augmented by 500 mM K(+) ions. The activity was unstable above 40 degrees C although some activity remained after heating and at 100 degrees C for 30s.