Mo-CBP(3), an Antifungal Chitin-Binding Protein from Moringa oleifera Seeds, Is a Member of the 2S Albumin Family

Mo-CBP(3) is a chitin-binding protein from M. oleifera seeds that inhibits the germination and mycelial growth of phytopathogenic fungi. This protein is highly thermostable and resistant to pH changes, and therefore may be useful in the development of new antifungal drugs. However, the relationship of MoCBP3 with the known families of carbohydrate-binding domains has not been established. In the present study, full-length cDNAs encoding 4 isoforms of Mo-CBP(3) (Mo-CBP(3)-1, Mo-CBP(3)-2, Mo-CBP(3)-3 and Mo-CBP(3)-4) were cloned from developing seeds. The polypeptides encoded by the Mo-CBP(3) cDNAs were predicted to contain 160 (Mo-CBP(3)-3) and 163 amino acid residues (Mo-CBP(3)-1, Mo-CBP(3)-2 and Mo-CBP(3)-4) with a signal peptide of 20-residues at the N-terminal region. A comparative analysis of the deduced amino acid sequences revealed that Mo-CBP(3) is a typical member of the 2S albumin family, as shown by the presence of an eight-cysteine motif, which is a characteristic feature of the prolamin superfamily. Furthermore, mass spectrometry analysis demonstrated that Mo-CBP(3) is a mixture of isoforms that correspond to different mRNA products. The identification of Mo-CBP(3) as a genuine member of the 2S albumin family reinforces the hypothesis that these seed storage proteins are involved in plant defense. Moreover, the chitin-binding ability of Mo-CBP(3) reveals a novel functionality for a typical 2S albumin.