New Insights into the Structure and Mode of Action of Mo-CBP(3), an Antifungal Chitin-Binding Protein of Moringa oleifera Seeds

Mo-CBP(3) is a chitin-binding protein purified from Moringa oleifera Lam. seeds that displays inhibitory activity against phytopathogenic fungi. This study investigated the structural properties and the antifungal mode of action of this protein. To this end, circular dichroism spectroscopy, antifungal assays, measurements of the production of reactive oxygen species and microscopic analyses were utilized. Mo-CBP(3) is composed of 30.3% α-helices, 16.3% β-sheets, 22.3% turns and 30.4% unordered forms. The Mo-CBP(3) structure is highly stable and retains its antifungal activity regardless of temperature and pH. Fusarium solani was used as a model organism for studying the mechanisms by which this protein acts as an antifungal agent. Mo-CBP(3) significantly inhibited spore germination and mycelial growth at 0.05 mg.mL(−1). Mo-CBP(3) has both fungistatic and fungicidal effects, depending on the concentration used. Binding of Mo-CBP(3) to the fungal cell surface is achieved, at least in part, via electrostatic interactions, as salt was able to reduce its inhibitory effect. Mo-CBP(3) induced the production of ROS and caused disorganization of both the cytoplasm and the plasma membrane in F. solani cells. Based on its high stability and specific toxicity, with broad-spectrum efficacy against important phytopathogenic fungi at low inhibitory concentrations but not to human cells, Mo-CBP(3) has great potential for the development of new antifungal drugs or transgenic crops with enhanced resistance to phytopathogens.