Carbohydrate specificity of a lectin isolated from the fungus Sclerotium rolfsii

In order to investigate the functional roles of a phytopathogenic fungal le ctin (SRL) isolated from the bodies of Sclerotium rolfsii, the binding prop erties of SRL were studied by enzyme linked lectinosorbent assay and by inh ibition of SRL-glycan interaction. Among glycoproteins(gp) tested for bindi ng, SRL reacted strongly with GalNAc alpha1 --> Ser/Thr (Tn) and /or Gal be ta1 --> 3GalNAc alpha1 --> (T-alpha) containing gps: human T-alpha and Tn g lycophorin, asialo salivary gps, and asialofetuin, but its reactivity towar d sialylated glycoproteins was reduced significantly. Of the sugar ligands tested for inhibition of SRL-asialofetuin binding, Thomsen-Friedenreich res idue (T-alpha) was the best, being 22.4 and 2.24X10(3) more active than Gal NAc and Gal beta1 --> residues, respectively. Other ligands tested were ina ctive. When the glycans used as inhibitors, T-alpha and/or Tn containing gp s, especially asialo PSM, asialo BSM, asialo OSM, active antifreeze gp, asi alo glycophorin and Tn-glycophorin were very active, and 1.0X10(4) times mo re potent than GalNAc. From these results, it is clear that the combining s ite of SRL should be of a cavity type and recognizes only Tn and T-alpha re sidues of glycans; it is suggested that T-alpha and Oy Tn glycotopes, which are present only in abnormal carbohydrate sequences of higher orders of ma mmal, are the most likely sites for phytopathogenic fungal attachment as an initial step of infection. The affinity of SRL for ligands can be ranked i n decreasing order as follows: multivalent T-alpha and Tn > > monomeric T-a lpha and Tn > GalNAc > > > II (Gal beta1 --> 4GlcNAc), L (Gal beta1 --> 4Gl c), and Gal. (C) 2001 Elsevier Sciences Inc. All rights reserved.