Adsorption Behavior of Hydrophobin Proteins on Polydimethylsiloxane Substrates

The design of a bioactive surface with appropriate wettability
for effective protein immobilization has attracted much attention.
Previous experiments showed that the adsorption of hydrophobic protein
HFBI onto a polydimethylsiloxane (PDMS) substrate surface can reverse
the inherent hydrophobicity of the surface, hence making it suitable
for immobilization of a secondary protein. In this study, atomistic
molecular dynamics simulations have been conducted to elucidate the
adsorption mechanism of HFBI on the PDMS substrate in an aqueous environment.
Nine independent simulations starting from three representative initial
orientations of HFBI toward the solid surface were performed, resulting
in different adsorption modes. The main secondary structures of the
protein in each mode are found to be preserved in the entire course
of adsorption due to the four disulfide bonds. The relative binding
free energies of the different adsorption modes were calculated, showing
that the mode, in which the binding residues of HFBI fully come from
its hydrophobic patch, is most energetically favored. In this favorable
binding mode, the hydrophilic region of HFBI is fully exposed to water,
leading to a high hydrophilicity of the modified PDMS surface, consistent
with experiments. Furthermore, a set of residues consisting of Leu12,
Leu24, Leu26, Ile27, Ala66, and Leu68 were found to play an important
role in the adsorption of HFBI on different hydrophobic substrates,
irrespective of the structural features of the substrates.