Investigation of the role hydrophobin monomer loops using hybrid models via molecular dynamics simulation

Hydrophobins are small amphiphilic fungal proteins that are highly surface-active and are used in various industrial applications such as dispersion, immobilization, and antifouling. At hydrophobic-hydrophilic interfaces, hydrophobins tend to self-assemble as rodlets or monolayers, depending on whether they are class I or II. Several studies have determined the three-dimensional structure and investigated the self-assembly formation mechanism of the class I EAS from Neurospora crassa and the class II HFBII from Trichoderma reesei. Although some studies have examined the performance of chimeric hydrophobins, they have not been investigated at the atomic scale. Here, we designed chimeric hydrophobins by grafting the L₁ loop of Vmh2 and the L₃ loop of EAS onto the class II hydrophobin HFBII by homology modeling and performed vacuum-water interface molecular simulations to determine their structural behaviors. We found that the chimeric hydrophobin grafted with the L₃ of EAS became unstable under standard conditions, whereas that grafted with the L₁ of Vmh2 became unstable in the presence of calcium ions. Moreover, when both the EAS L₃ and Vmh2 L₁ were grafted together, the structure became disordered and lost its amphiphilic characteristics in standard conditions. In the presence of calcium, however, its structural stability was restored. However, an additional external perturbation is required to trigger the conformational transition. Although our chimeric hydrophobin models were designed through homology modeling, our results provide detailed information regarding hydrophobin self-assembly and their surface-interactive behavior that may serve as a template for designing hydrophobins for future industrial applications.