Cerato-Populin and Cerato-Platanin, Two Non-Catalytic Proteins from Phytopathogenic Fungi, Interact with Hydrophobic Inanimate Surfaces and Leaves

Based on sequence homology, several fungal Cys-rich secreted proteins have been grouped in the ceratoplatanin (CP) family, which comprises at least 40 proteins involved mainly in eliciting defense-related responses. The core member of this family is cerato-platanin, a moderately hydrophobic protein with a double w–b barrel fold. CP and the recently identified orthologous cerato-populin (Pop1) are involved in host–fungus interaction, and can be considered non-catalytic fungal PAMPs. CP is more active in inducing defense when in an aggregated conformation than in its native form, but little is known about other CP-orthologous proteins. Here, we cloned, expressed, and purified recombinant Pop1, which was used to characterize the protein aggregates. Our results suggest that the unfolded, self-assembled Pop1 is more active in inducing defense, and that the unfolding process can be induced by interaction with hydrophobic inanimate surfaces such as Teflon, treated mica, and gold sheets. In vivo, we found that both CP and Pop1 interact with the hydrophobic cuticle of leaves. Therefore, we propose that the interaction of these proteins with host cuticle waxes could induce unfolding and consequently trigger their PAMP-like activity.