Purification and characterization of an antifungal PR-5 protein from pumpkin leaves

A 28-kDa antifungal PR-5 protein (PLTP) was purified from pumpkin leaves to homogeneity by using ammonium sulfate fractionation, a regenerated chitin column, and reversed-phase column chromatographies on butyl-Toyopearl and HPLC C18 columns. Analysis of 14 N-terminal amino acid sequences of PLTP shows 100% sequence identity to those of two PR-5 proteins, NP24 from tomatoes and AP24 from tobacco. The identical sequence also exhibited high amino acid sequence homology to that of an osmotin-like protein (OLP; 71%) from tobacco cells and thaumatin (64%), a sweet-tasting protein of Thaumatococcus danielli Bench. When the PLTP was immuno-blotted with antiserum raised against the tobacco OLP, the OLP antibody specifically cross-reacted with the PLTP, suggesting that they share several common epitopes in their tertiary structure of the proteins. The purified PLTP rapidly lyzed hyphal tips of Neurospora crassa at a concentration greater than 200 nM and significantly inhibited the fungal growth of Fusarium oxysporum in an agar-disc plate at a concentration greater than 2 microM. It also shows a synergistic effect with nikkomycin, a chitin synthase inhibitor, for the growth inhibition of Candida albicans.