Binding specificity of philyra pisum lectin to pathogen-associated molecular patterns, and its secondary structure

Abstract

We recently reported a Philyra pisum lectin (PPL) that exerts mitogenic effects on human lymphocytes, and its molecular characterization. The present study provides a more detailed characterization of PPL based on the results from a monosaccharide analysis indicating that PPL is a glycoprotein, and circular dichroism spectra revealing its estimated a-helix, β -sheet, β -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, lipopolysaccharide from Gram-negative bacteria, and both mannan and β -1,3-glucan from fungi. PPL binds to lipoteichoic acids and mannan, but not to lipopolysaccharides or β -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 a-helix and β -structures, respectively. These properties are inherent to the innate immune system of P. pisum and indicate that PPL could be involved in signal transmission into Gram-positive bacteria or fungi.