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

Abstract 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 A resolution to a crystallographic R -factor of 21%. Each subunit displays the thirteen-stranded β-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.