Purification and characterization of a lectin from the seeds of Erythrina costaricensis

Abstract

This work compares three methods used for the purification of the lectin of Erythrina costaricensis and presents new data regarding its physicochemical properties and N-terminal sequence. The lectin was isolated from the seeds of Erythrina costaricensis using O-alpha-D galactosyl polyacrylamide, galactose-derivatized Sepharose and ConA-Sepharose as affinity chromatography supports. The lectin content is about 110 mg/100 g dry flour. The protein agglutinates human and rabbit erythrocytes; other animal erythrocytes were not agglutinated. The agglutination is inhibited by galactosyl moieties, p-nitrophenyl-beta-galactoside being the strongest inhibitor. The lectin is a dimeric protein (56 kDa) with identical subunits, each with a mol. wt of 27.2 kDa. The lectin is a glycoprotein with 3.6% neutral sugars. The amino acid content shows a high proportion of acidic and hydroxy residues; cysteine is absent and there are 6 methionines/mol protein. The N-terminal sequence is similar to those of Erythrina lectins; Ala is the N-terminal amino acid. In summary this paper reports the isolation of a lectin which shares many structural and functional properties with other Erythrina lectins. However, differences in some of its characteristics (pI, interactions with animal erythrocytes, mitogenic ability) indicate some distinctions in structure amongst this group of proteins.