Direct and cross-recognition of lichenized Trebouxia Puymaly (Chlorophyta, Trebouxiophyceae) and Nostoc Vaucher ex Bornet (Cyanobacteria, Cyanophyceae) by their homologous and heterologous fungal lectins

In this study, we have used affinity chromatography to purify the lectins from a chlorolichen, Evernia prunastri (L.) Ach., and a cyanolichen, Peltigera canina (Ach.) Schard. These species secrete lectins that display arginase activity in addition to their role as recognition proteins. We found that fluorescently labeled lectins display efficient binding to their ligands on the cell wall. Binding was stronger when the lectin reacted with the producing (homologous) photobiont (alga or cyanobacteria) than with the nonproducing (heterologous) species used throughout the study. To address the specificity of lectin binding, we performed desorption experiments of cell-bound lectins with different hexoses. We found that Evernia lectin is only desorbed by galactose, consistent with its specific binding to a single polygalactosylated ligand. Conversely, Peltigera lectin is desorbed not only by galactose, but also by mannose. This indicates that Peltigera lectin recognizes not only α-d-galactose-containing ligands, but also ligands containing α-d-mannose moieties.