CARBOHYDRATE-BINDING SPECIFICITY OF TETRACARPIDIUM-CONOPHORUM LECTIN

The carbohydrate-binding specificity of a novel plant lectin isolated from the seeds of Tetracarpidium conophorum (Nigerian walnut) has been studied by quantitative hapten inhibition assays and by determining the behavior of a number of oligosaccharides and glycopeptides on lectin-Sepharose affinity columns. The Tetracarpidium lectin shows preference for simple, unbranched oligosaccharides containing a terminal Gal-beta-1 --> 4GlcNAc sequence over a Gal-beta-1 --> 3GlcNAc sequence and substitution by sialic acid or fucose of the terminal galactose residue, the subterminal N-acetylglucosamine or more distally located sugar residues of oligosaccharides reduce binding activity. Branched complex-type glycans containing either Gal-beta-1 --> 4GlcNAc or Gal-beta-1 --> 3GlcNAc termini bind with higher affinity than simpler oligosaccharides. The lectin shows highest affinity for a tri-antennary glycan carrying Gal-beta-1 --> 4GlcNAc substituents on C-2 and C-4 of Man-alpha-1 --> 3 and C-2 of Man-alpha-1 --> 6 core residues. Bi-and tri-glycans lacking this branching pattern bind more weakly. Tetra-antennary glycans and mono- and dibranched hybrid-type glycans also bind weakly to the immobilized lectin. Therefore, Tetracarpidium lectin complements the binding specificities of well-known lectins such as Datura stramonium agglutinin, Phaseolus vulgaris agglutinin, and lentil lectin and will be a useful additional tool for the identification and separation of complex-type glycans.