Chemical characterization of the lectin from Amaranthus leucocarpus syn. hypocondriacus by 2-D proteome analysis

In this work, we characterized chemically the N-acetyl-D-galactosamine specific lectin from Amaranthus leucocarpus syn hypocondriacus lectin (ALL). It is a dimeric glycoprotein composed by three isoforms with pl at 4.8, 4.9, and 5.2. Circular dichroism analysis indicated that the secondary structure of ALL contains 45% of -sheet and 5% of -helix. Amino acid sequence of the purified lectin and its isoforms was determined from peptides obtained after trypsin digestion by MALDI-TOF (Matrix assisted laser desorption ionization-time of flight). The tryptic peptides prepared from the purified lectin and the three isoforms showed different degrees (80 to 83%) of identity with the amino acid sequence belonging to a previously described high nutritional value protein from A. hypocondriacus not shown at the time to be a lectin. Furthermore, analysis of tryptic peptides obtained from ALL previously treated with peptide N-glycosidase, revealed a 93% identity with the aforementioned protein. Presence of N-glycosidically linked glycans of the oligomannosidic type and, in minor proportion, of the N-acetyllactosaminic type glycans was determined by affinity chromatography on immobilized Con A.