Molecular dynamics study of the folding of hydrophobin SC3 at a hydrophilic/hydrophobic interface

Hydrophobins are fungal proteins that self-assemble at hydrophilic/hydrophobic interfaces into amphipathic membranes. These assemblages are extremely stable and posses the remarkable ability to invert the polarity of the surface on which they are adsorbed. Neither the three-dimensional structure of a hydrophobin nor the mechanism by which they function is known. Nevertheless, there are experimental indications that the self-assembled form of the hydrophobins SC3 and EAS at a water/air interface is rich with beta-sheet secondary structure. In this paper we report results from molecular dynamics simulations, showing that fully extended SC3 undergoes fast (approximately 100 ns) folding at a water/hexane interface to an elongated planar structure with extensive beta-sheet secondary elements. Simulations in each of the bulk solvents result in a mainly unstructured globular protein. The dramatic enhancement in secondary structure, whether kinetic or thermodynamic in origin, highlights the role interfaces between phases with large differences in polarity can have on folding. The partitioning of the residue side-chains to one of the two phases can serve as a strong driving force to initiate secondary structure formation. The interactions of the side-chains with the environment at an interface can also stabilize configurations that otherwise would not occur in a homogenous solution.