Purification, characterization and molecular cloning of a novel mannose-binding lectin from rhizomes of Ophiopogon japonicus with antiviral and antifungal activities

A novel mannose-binding lectin (designated OJL) was purified from rhizomes of Ophiopogon japonicus by ion exchange chromatography on DEAE-Sepharose and gel filtration on Sephacryl S-100. This novel lectin was a homodimer consisting of approximately 12 kDa subunits linked by non-covalent bonds. The hemagglutination activity of OJL was inhibited by Man-α(1,3:1,6)-mannotriose, Man-α(1,3)-Man, Man-α(1,6)-Man, Man-α(1,2)-Man, Me α-d-man and d-mannose. The hemagglutination activity was stable in the pH range of 5.0-9.0 and at temperatures below 60 °C. It was inhibitory to herpes simplex virus type II (HSV-II) with an EC50 of 3.93 μg/mL and showed antifungal activity against Gibberella saubinetii and Rhizoctonia solani. The full-length cDNA of OJL contained 704 bp with an open reading frame encoding a precursor protein of 170 amino acid residues. Molecular modeling studies demonstrated that OJL exhibits a very similar three-dimensional structure of the mannose-binding sites with other monocot mannose-binding lectins. Docking experiments further revealed that two of three putative mannose-binding sites of OJL are active. These results can be used to further explain the carbohydrate-binding activity and specific hemagglutinating activity. A model of the molecular evolution of the monocot mannose-binding lectins is proposed.