One-step purification of lectins from banana pulp using sugar-immobilized gold nano-particles.

To obtain lectins without tedious purification steps, we developed a convenient method for a one-step purification of lectins using sugar-immobilized gold nano-particles (SGNPs). Proteins in crude extracts from plant materials were precipitated with 60% ammonium sulphate, and the precipitate was re-dissolved in a small volume of phosphate buffer. The resultant solution was then mixed with appropriate SGNPs under an optimized condition. After incubating overnight at 4 degrees C, lectins in the mixture formed aggregate with SGNPs, which was visually detected and easily sedimented by centrifugation. The aggregate was dissolved by adding inhibitory sugars, which were identical to the non-reducing sugar moieties on the SGNPs. According to SDS-PAGE and MS of thus obtained proteins, it was found that SGNPs isolated lectins with a high purity. For example, a protein isolated from banana using Glcalpha-GNP (alpha-glucose-immobilized gold nano-particle) was identified as banana lectin by trypsin-digested peptide-MS finger printing method.