Characterization of isolectins in Tetracarpidium conophorum seeds (Nigerian walnut)

A lectin preparation obtained from Tetracarpidium conophorum (Nigerian walnut) by affinity chromatography of seed extracts on lactose-agarose has been shown to contain two components by gel filtration on Sephadex G150. The larger component Tetracarpidium conophorum agglutinin I (TCAI) is a disulphide-bonded 70 kDa homodimer whereas the second component TCAII is a 34 kDa monomeric protein. Amino terminal aminoacid sequencing shows identity in TCAI and TCAII for the first fifteen residues after which the sequences diverge. The N-terminal sequences of TCAI and TCAII show identity with sequences in the B-chains of ricin and Ricinus communis agglutinin I (RCAI) in eleven of the initial fifteen residues. Thereafter TCAI appears to be homologous to the ricin B chain whereas TCAII is more homologous with the B chain of RCAI. A limited screening of the carbohydrate-binding specificity of TCAII by affinity chromatography of defined oligosaccharides on TCAII Sepharose columns shows that the binding specificity reported earlier for affinity purified Tetracarpidium conophorum isolectins (Sato S, Animashaun T, Hughes RC (1991) J Biol Chem 266:11485-94) reflects the binding properties of TCAII which is the major isolectin in unfractionated lectin preparations.