Binding Specificity of Philyra pisum Lectin to Pathogen-Associated Molecular Patterns, and Its Secondary Structure

Binding Specificity of Philyra pisum Lectin to Pathogen-Associated Molecular Patterns, and Its Secondary Structure

We recently reported a Philyra pisum lectin (PPL) that exerts mitogenic effects on human lym-phocytes, and its molecular characterization. The present study provides a more detailed charac-terization of PPL based on the results from a monosaccharide analysis indicating that PPL is a glycoprotein, and circular dichroism spectra revealing its estimated <em>α</em>-helix,<em> β</em>-sheet,<em> β</em>-turn, and random coil contents to be 14.0%, 39.6%, 15.8%, and 30.6%, respectively. These contents are quite similar to those of deglycosylated PPL, indicating that glycans do not affect its intact structure. The binding properties to different pathogen-associated molecular patterns were investigated with hemagglutination inhibition assays using lipoteichoic acid from Gram-positive bacteria, lipopoly-saccharide from Gram-negative bacteria, and both mannan and<em> β</em>-1,3-glucan from fungi. PPL binds to lipoteichoic acids and mannan, but not to lipopolysaccharides or<em> β</em>-1,3-glucan. PPL exerted no significant antiproliferative effects against human breast or bladder cancer cells. These results indicate that PPL is a glycoprotein with a lipoteichoic acid or mannan-binding specificity and which contains low and high proportions of <em>α</em>-helix and<em> β</em>-structures, respectively. These properties are inherent to the innate immune system of <em>P. pisum</em> and indicate that PPL could be involved in signal transmission into Gram-positive bacteria or fungi.