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Adsorption, Folding, and Packing of an Amphiphilic Peptide at the Air/Water Interface
journal contribution
posted on 2016-02-22, 05:02 authored by Ozge Engin, Mehmet SayarPeptide oligomers play an essential role as model compounds
for identifying key motifs in protein structure formation and protein
aggregation. Here, we present our results, based on extensive molecular
dynamics simulations, on adsorption, folding, and packing within a
surface monolayer of an amphiphilic peptide at the air/water interface.
Experimental results suggest that these molecules spontaneously form
ordered monolayers at the interface, adopting a β-hairpin-like
structure within the surface layer. Our results reveal that the β-hairpin
structure can be observed both in bulk and at the air/water interface.
However, the presence of an interface leads to ideal partitioning
of the hydrophobic and hydrophilic residues, and therefore reduces
the conformational space for the molecule and increases the stability
of the hairpin structure. We obtained the adsorption free energy of
a single β-hairpin at the air/water interface, and analyzed
the enthalpic and entropic contributions. The adsorption process is
favored by two main factors: (1) Free-energy reduction due to desolvation
of the hydrophobic side chains of the peptide and release of the water
molecules which form a cage around these hydrophobic groups in bulk
water. (2) Reduction of the total air/water contact area at the interface
upon adsorption of the peptide amphiphile. By performing mutations
on the original molecule, we demonstrated the relative role of key
design features of the peptide. Finally, by analyzing the potential
of mean force among two peptides at the interface, we investigated
possible packing mechanisms for these molecules within the surface
monolayer.