Ion-specific induced fluctuations and free energetics of aqueous protein hydrophobic interfaces: toward connecting to specific-ion behaviors at aqueous liquid-vapor interfaces.
We explore anion-induced interface fluctuations near protein-water interfaces using coarse-grained representations of interfaces as proposed by Willard and Chandler ( J. Phys. Chem. B 2010 , 114 , 1954 - 1958 ). We use umbrella sampling molecular dynamics to compute potentials of mean force along a reaction coordinate bridging the state where the anion is fully solvated and one where it is biased via harmonic restraints to remain at the protein-water interface. Specifically, we focus on fluctuations of an interface between water and a hydrophobic region of hydrophobin-II (HFBII), a 71 amino acid residue protein expressed by filamentous fungi and known for its ability to form hydrophobically mediated self-assemblies at interfaces such as a water/air interface. We consider the anions chloride and iodide that have been shown previously by simulations as displaying specific-ion behaviors at aqueous liquid-vapor interfaces. We find that as in the case of a pure liquid-vapor interface, at the hydrophobic protein-water interface, the larger, less charge-dense iodide anion displays a marginal interfacial stability compared with that of the smaller, more charge-dense chloride anion. Furthermore, consistent with the results at aqueous liquid-vapor interfaces, we find that iodide induces larger fluctuations of the protein-water interface than chloride.
Department of Chemistry and Biochemistry and ‡Department of Chemical and Biomolecular Engineering, University of Delaware , Newark, Delaware 19716, United States.
Di
D
Cui
Shuching
S
Ou
Eric
E
Peters
Sandeep
S
Patel
D005656:Fungal Proteins / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D011189:Potassium Chloride / Q000737:chemistry; D011193:Potassium Iodide / Q000737:chemistry; D011487:Protein Conformation; D013816:Thermodynamics; D014835:Volatilization; D014867:Water / Q000737:chemistry*
D005656:Fungal Proteins; D014867:Water; D011193:Potassium Iodide; D011189:Potassium Chloride