Isolation and characterization of an N-acetylgalactosamine specific lectin from Salvia sclarea seeds

Abstract

Crude extracts from Salvia sclarea seeds were known to contain a lectin which specifically agglutinates Tn erythrocytes (Bird, G. W. G., and Wingham, G. (1974) Vox Sang. 26, 163-166). We have purified the lectin to homogeneity by ion-exchange chromatography and affinity chromatography. The agglutinin was found to be a glycoprotein of Mr = 50,000, composed of two identical subunits of Mr = 35,000 linked together by disulfide bonds. The purified lectin agglutinates specifically Tn erythrocytes and, at higher concentrations, also Cad erythrocytes. Native A, B, or O red blood cells are not agglutinated by the lectin and, even after treatment with sialidase or papain, these cells are not recognized. Tn red cells present 1.45 X 10(6) accessible sites to the lectin which binds to these erythrocytes with an association constant of 1.8 X 10(6) M-1. On Cad red cells, 1.73 X 10(6) sites are accessible to the lectin which binds with an association constant of 1.0 X 10(6) M-1. The carbohydrate specificity of the S. sclarea lectin has been determined in detail, using well defined monosaccharide, oligosaccharide, and glycopeptide structures. The lectin was found to be specific for terminal N-acetylgalactosamine (GalNAc) residues. It binds preferentially alpha GalNAc determinants either linked to Ser or Thr (as in Tn structures) or linked in 1-3 to a beta GalNAc or to an unsubstituted beta Gal. Although more weakly, the lectin binds beta GalNAc residues linked in 1-4 to a beta Gal (as in Cad structures). It does not recognize beta GalNAc determinants linked in 1-3 to a Gal (as in globoside) or the alpha GalNAc residues of blood group A structures.