Characterizing the structure and assembly features of class IB hydrophobins

Abstract

Hydrophobins are small, amphiphilic proteins secreted by filamentous fungi that accumulate at hydrophobic-hydrophilic interfaces and self-assemble into rodlets, resilient repeating β-sheet structures that reverse the wettability of surfaces. Their versatility makes them desirable targets for engineered applications, however our limited understanding of how hydrophobins function and self-assemble slows efforts. To better understand the mechanism and characteristics of self-assembly, three diverse hydrophobins were structurally and functionally characterized. These hydrophobins share a tertiary structure, however their surface charge and hydrophobicity vary, particularly in how well-defined the hydrophobic surface patch is. They undergo a conformational change upon rodlet self-assembly involving the first inter-cysteine loop, loss of α-helicity, and gain of β-sheet character. I propose a model for hydrophobin surface-association and self-assembly, where distinct hydrophobic patches and the isoelectric point of a hydrophobin influence its optimal conditions for self-assembly, contributing to hydrophobin engineering with potential for a plethora of industries and applications.