Amino acid sequence and some properties of lectin-D from the roots of pokeweed (Phytolacca americana).

Two pokeweed lectins, designated PL-D1 and PL-D2, have been isolated from the roots of pokeweed (Phytolacca americana) using chitin affinity column chromatography followed by gel filtration on a Sephacryl S-200 column and fast protein liquid chromatography on a Mono-Q column, and their amino acid sequences have been analyzed. PL-D1 consists of 84 amino acid residues and has a molecular mass of 9317, while PL-D2 has an identical sequence with PL-D1 except lack of the C-terminal Leu-Thr. PL-D is composed of two chitin-binding domains, A and B, with 50% homology with each other. Both PL-Ds did not agglutinate native rabbit erythrocytes, but showed about 0.1% of the agglutinating activity of wheat germ agglutinin toward trypsin-treated erythrocytes. In the presence of beta (1-->4) linked oligomers of N-acetyl-D-glucosamine, which inhibit the hemagglutination, PL-D1 had an ultraviolet-difference spectrum with maxima at 292-294 nm and 284-285 nm, attributed to the red shift of the tryptophan residue, suggesting the location of tryptophan residue(s) at or near saccharide-binding site of PL-D1.