A HIGH-DEGREE OF SEQUENCE HOMOLOGY IN THE PUTATIVE CARBOHYDRATE-RECOGNITION DOMAINS OF POKEWEED MITOGEN AND WHEAT-GERM-AGGLUTININ - POLY-N-ACETYLLACTOSAMINE-BINDING LECTINS FROM DIFFERENT SPECIES

The complete amino acid sequence of a poly-N-acetyllactosamine-binding pokeweed mitogen 4 (Pa-4) was determined using a protein sequencer. After digestion of Pa-4 with endoproteinase Lys-C, Asp-N, Arg-C or Glu-C, the resulting peptides were separated by reversed-phase high-performance liquid chromatography (HPLC) and then subjected to sequence analysis using a protein sequencer. The complete amino acid sequence of Pa-4 was found to exhibit a high degree of homology with that of wheat germ agglutinin (WGA) regarding their overall sequences and the spatial arrangement of cysteine-glycine. Furthermore, the amino acid residues of WGA directly involved in carbohydrate-binding sites were found in the homologous region in Pa-4, This is the first report to show that lectins from different plant families (Phytolaccaceae for Pa-4 and Gramineae for WGA) possess homologous primary sequences.