A novel tetrameric lectin from Lycoris aurea with four mannose binding sites per monomer

The mannose-binding agglutinin from bulbs of Lycoris aurea (LAA) agglutinates rabbit but not human erythrocytes. The molecular mass of the monomer in SDS/PAGE is 12 kDa while the apparent molecular mass in gel filtration is 48 kDa, indicating that LAA is a homotetramer. The full-length cDNA of LAA contains 683 bp with an open reading frame encoding a protomer of 162 amino-acid residues. Hydrophobic Cluster Analysis and molecular modeling of the 109-residue mature polypeptide suggested a similar secondary and tertiary structure to those of Narcissus pseudonarcissus agglutinin (NPA). Molecular docking revealed that, besides the three mannose-binding sites common among Amaryllidaceae lectins, LAA also contains a fourth unique mannose-binding site formed by a tryptophan cluster. The existence of four mannose-binding sites in each monomer of LAA is very unusual and has only been reported for NPA earlier.