Self-assembly at Air/Water Interfaces and Carbohydrate Binding Properties of the Small Secreted Protein EPL1 from the fungus Trichoderma atroviride

Abstract

The protein EPL1 from the fungus Trichoderma atroviride belongs to the cerato-platanin protein family. These proteins occur only in filamentous fungi and are associated with the induction of defense responses in plants and allergic reactions in humans. However, fungi with other life-styles also express cerato-platanin proteins, and the primary function of this protein family has not been elucidated yet. In this study we investigated the biochemical properties of the cerato-platanin protein EPL1 from T. atroviride. Our results showed that EPL1 readily self-assembles at air/water interfaces and forms protein layers that can be re-dissolved in water. These properties are reminiscent of hydrophobins, which are amphiphilic fungal proteins that accumulate at interfaces. AFM imaging showed that EPL1 assembles into irregular meshwork-like substructures. Further, surface activity measurements with EPL1 revealed that, in contrast to hydrophobins, it increases the polarity of aqueous solutions and surfaces. In addition, EPL1 was found to bind to various forms of polymeric chitin. The T. atroviride genome contains three epl-genes. epl1 was predominantly expressed during hyphal growth, whereas epl2 was mainly expressed during spore formation, suggesting that the respective proteins are involved in different biological processes. For epl3 no gene expression was detected under most growth conditions. Single and double gene knockout strains of epl1 and epl2 did not reveal a detectable phenotype, which shows that these proteins are not essential for fungal growth and development, despite their abundant expression.