The lectin from the mushroom, P. velutina (PVL), recognizes specifically N-acetylglucosamine- and N-acetylneuraminic acid-contg. glycans. Here, the crystal structure of the 401-amino-acid-residue PVL was detd., and showed that it adopted a very regular 7-bladed b-propeller fold with the N-terminal region tucked into the central cavity around the pseudo-7-fold axis. In a complex of PVL with N-acetylglucosamine, 6 monosaccharides were found to be bound in pockets located between 2 consecutive propeller blades. Due to the repeats shown by the sequence, the binding sites were very similar. Five H-bonds between the protein and the sugar OH and N-acetyl groups stabilized the complex, together with the hydrophobic interactions with conserved Tyr and His residues. A complex of PVL with N-acetylneuraminic acid showed mol. mimicry with the same H-bond network, but with different orientations of the carbohydrate ring in the binding site. The b-hairpin loops connecting the 2 inner b-strands of each blade were metal cation-binding sites and 2-3 Ca2+ ions were located in the structure. The multi-specificity and high multi-valency of PVL, combined with its similarity to the extracellular domain of an important class of cell adhesion mols., integrins, were another example of the outstanding success of b-propeller structures as mol. binding machines in nature. [on SciFinder (R)]