Amino acid sequence and three-dimensional structure of the Tn-specific isolectin B4 from Vicia villosa

The partial amino acid sequence of the tetrameric isolectin B4 from Vicia villosa seeds has been determined by peptide analysis, and its three-dimensional structure solved by molecular replacement techniques and refined at 2.9 Angstrom resolution to a crystallographic R-factor of 21%. Each subunit displays the thirteen-stranded beta-barrel topology characteristic of legume lectins, The amino acid residues involved in metal- and sugar-binding are similar to those of other GalNAc-specific lectins, indicating that residues outside the carbohydrate-binding pocket modulate the affinity for the Tn glycopeptide, Isolectin B4 displays an unusual quaternary structure, probably due to protein glycosylation. (C) 1997 Federation of European Biochemical Societies.