Self-assembled structures of class I hydrophobin RolA from the fungus Aspergillus oryzae on PTFE surfaces in the absence of an air-water interface

Class I hydrophobins secreted by filamentous fungi self-assemble at interfaces to form rod-like structures known as rodlets. Although hydrophobins can self-assemble at both air-water and solid-water interfaces, the mechanism governing the latter self-assembly remains poorly understood. In this study, we investigated the self-assembly of RolA, a class I hydrophobin from Aspergillus oryzae, on a polytetrafluoroethylene (PTFE) surface without an air-water interface. The fluorescence time course of thioflavin T binding indicated that RolA self-assembled at the solid-water interface. Atomic force microscopy revealed that RolA formed both rod-like structures and amorphous aggregates. The presence of such aggregates, not observed at air-water interfaces, suggests that the self-assembly pathway depends on the interface type. These findings help to advance our understanding of how the functions of hydrophobins at solid-water interfaces are related to hydrophobin self-assembly.