Purification and characterization of three antifungal proteins from cheeseweed (Malva parviflora)

Three potent antimicrobial proteins were purified from cheeseweed (Malva parviflora) seeds. These antimicrobial proteins, named CW-3, CW-4, and CW-5, showed different antimicrobial spectrum and potency compared to the two heterologous antimicrobial proteins (CW-1 and CW-2) purified previously. CW-3 and CW-4 possess antimicrobial activities against Phytophthora infestans (Pi), but not Fusarium graminearum (Fg). A database search indicated that CW-3 shares high homology to cotton vicilin, an abundant seed storage protein. CW-4 shares homology to 2S albumin, another seed storage protein from cotton. CW-5 has antimicrobial activity against Fg, but no activity against Pi was observed at protein concentration up to 50 ppm. Under low salt condition, CW-5 showed potent antimicrobial activity against Fg, but under high salt condition, the antimicrobial activity was drastically diminished. Database search indicated that CW-5 has high homology to a lipid transfer protein from grape. The IC(50) values of the three purified antimicrobial proteins under both low and high salt conditions were determined. The isolation of five antimicrobial proteins for the first time from a single plant source provides further understanding of the plant innate defense system and insight on how plants evolve their complex and complementary antimicrobial system that is important in the early stage of development.