INTERACTION OF LINEAR MANNO-OLIGOSACCHARIDES WITH 3 MANNOSE-SPECIFIC BULB LECTINS - COMPARISON WITH MANNOSE GLUCOSE-BINDING LECTINS

Three new mannose-binding lectins, isolated from daffodil (NPA), amaryllis (HHA), and snowdrop (GNA) bulbs, are capable of precipitating with a linear mannopentaose (Man-alpha-1-3Man-alpha-1-3Man-alpha-1-2Man). NPA and HHA reacted strongly with the mannopentaose whereas GNA gave a precipitate only at concentrations > 500-mu-M. A phosphate group at C-6 of the nonreducing terminal mannosyl group prevented precipitation in all three cases. The reduced (NaBH4) mannopentatose, Man4Man-ol, did not precipitate with GNA or NPA, but was active with HHA. This activity was lost when Man4Man-ol was converted (NaIO4 then NaBH4; mild acid hydrolysis of the reduced product) into trisaccharide derivatives. With alpha-D-Man p-OMe the three lectins gave UV difference spectra having large positive peaks at 292-293 and 283-284 nm, and a small positive peak at 275 nm. characteristic of tryptophanyl and tyrosyl residues. The association constants for the interaction with alpha-D-Man p-OMe were very low (NPA, 86; HHA, 66; and GNA, 41 M-1, but the lectins bound methyl (1 --> 3)-alpha-mannobioside with increased affinity (K for NPA 540. for HHA 2400, and for GNA 200 M-1). The bulb lectins lack binding sites for hydrophobic ligands, as judged by their failure to interact with the fluorescent probes 8-anilino-1-naphthalenesulfonic acid (ANS) and 6-p-toluidino-2-naphthalenesulfonic acid (TNS).