Adsorption Kinetics and Self-Assembled Structures of Aspergillus oryzae Hydrophobin RolA on Hydrophobic and Charged Solid Surfaces.

Hydrophobins are small secreted amphipathic proteins ubiquitous among filamentous fungi. Hydrophobin RolA produced by Aspergillus oryzae attaches to solid surfaces, recruits polyesterase CutL1, and thus promotes hydrolysis of polyesters. Because the N-terminal region of RolA is involved in the interaction with CutL1, the orientation of RolA on the solid surface is important. However, the kinetic properties of RolA adsorption to solid surfaces with various chemical properties remain unclear, and RolA structures assembled after the attachment to surfaces are unknown. Using a quartz crystal microbalance (QCM), we analyzed the kinetic properties of RolA adsorption to the surfaces of QCM electrodes that had been chemically modified to become hydrophobic or charged. We also observed the assembled RolA structures on the surfaces by atomic force microscopy and performed molecular dynamics (MD) simulations of RolA adsorption to self-assembled monolayer (SAM)-modified surfaces. The RolA-surface interaction was considerably affected by the zeta potential of RolA, which was affected by pH. The interactions of RolA with the surface seemed to be involved in the self-assembly of RolA. Three types of self-assembled structures of RolA were observed: spherical, rod-like, and mesh-like. The kinetics of RolA adsorption and the structures formed depended on the amount of RolA adsorbed, chemical properties of the electrode surface, and the pH of the buffer. Adsorption of RolA to solid surfaces seemed to depend mainly on its hydrophobic interaction with the surfaces; this was supported by MD simulations, which suggested that hydrophobic Cys-Cys loops of RolA attached to all SAM-modified surfaces at all pH values.