Purification, Biochemical Characterization, and Bioactive Properties of a Lectin Purified from the Seeds of White Tepary Bean (Phaseolus Acutifolius Variety Latifolius)

Abstract

The present work shows the characterization of Phaseolus acutifolius varietylatifolius, on which little research has been published, and provides detailed information onthe corresponding lectin. This protein was purified from a semi-domesticated line of whitetepary beans from Sonora, Mexico, by precipitation of the aqueous extract with ammoniumsulfate, followed by affinity chromatography on an immobilized fetuin matrix. MALDITOF analysis of Phaseolus acutifolius agglutinin (PAA) showed that this lectin iscomposed of monomers with molecular weights ranging between 28 and 31 kDa. At highOPEN ACCESSMolecules 2011, 162562salt concentrations, PAA forms a dimer of 63 kDa, but at low salt concentrations, thesubunits form a tetramer. Analysis of PAA on 2D-PAGE showed that there are mainlythree types of subunits with isoelectric points of 4.2, 4.4, and 4.5. The partial sequenceobtained by LC/MS/MS of tryptic fragments from the PAA subunits showed 90100%identity with subunits from genus Phaseolus lectins in previous reports. The tepary beanlectin showed lower hemagglutination activity than Phaseolus vulgaris hemagglutinin(PHA-E) toward trypsinized human A and O type erythrocytes. The hemagglutinationactivity was inhibited by N-glycans from glycoproteins. Affinity chromatography with theimmobilized PAA showed a high affinity to glycopeptides from thyroglobulin, which alsohas N-glycans with a high content of N-acetylglucosamine. PAA showed less mitogenicactivity toward human lymphocytes than PHA-L and Con A. The cytotoxicity of PAA wasdetermined by employing three clones of the 3T3 cell line, demonstrating variabilityamong the clones as follows: T4 (DI50 51.5 ?g/mL); J20 (DI50 275 ?g/mL), and N5 (DI5072.5 ?g/mL).