The dynamics of multimer formation of the amphiphilic hydrophobin protein HFBII

Hydrophobins are surface-active proteins produced by filamentous fungi. They have amphiphilic structures and form multimers in aqueous solution to shield their hydrophobic regions. The proteins rearrange at interfaces and self-assemble into films that can show a very high degree of structural order. Little is known on dynamics of multimer interactions in solution and how this is affected by other components. In this work we examine the multimer dynamics by stopped-flow fluorescence measurements and Förster Resonance Energy Transfer (FRET) using the class II hydrophobin HFBII. The half-life of exchange in the multimer state was 0.9 s at 22 °C with an activation energy of 92 kJ/mol. The multimer exchange process of HFBII was shown to be significantly affected by the closely related HFBI hydrophobin, lowering both activation energy and half-life for exchange. Lower molecular weight surfactants interacted in very selective ways, but other surface active proteins did not influence the rates of exchange. The results indicate that the multimer formation is driven by specific molecular interactions that distinguish different hydrophobins from each other.