Characterizing hydrophobicity of amino acid side chains in a protein environment via measuring contact angle of a water nanodroplet on planar peptide network.
Hydrophobicity of macroscopic planar surface is conventionally characterized by the contact angle of water droplets. However, this engineering measurement cannot be directly extended to surfaces of proteins, due to the nanometer scale of amino acids and inherent nonplanar structures. To measure the hydrophobicity of side chains of proteins quantitatively, numerous parameters were developed to characterize behavior of hydrophobic solvation. However, consistency among these parameters is not always apparent. Herein, we demonstrate an alternative way of characterizing hydrophobicity of amino acid side chains in a protein environment by constructing a monolayer of amino acids (i.e., artificial planar peptide network) according to the primary and the β-sheet secondary structures of protein so that the conventional engineering measurement of the contact angle of a water droplet can be brought to bear. Using molecular dynamics simulations, contact angles θ of a water nanodroplet on the planar peptide network, together with excess chemical potentials of purely repulsive methane-sized Weeks-Chandler-Andersen solute, are computed. All of the 20 types of amino acids and the corresponding planar peptide networks are studied. Expectedly, all of the planar peptide networks with nonpolar amino acids are hydrophobic due to θ [Formula: see text] 90°, whereas all of the planar peptide networks of the polar and charged amino acids are hydrophilic due to θ [Formula: see text] 90°. Planar peptide networks of the charged amino acids exhibit complete-wetting behavior due to θ [Formula: see text] 0°. This computational approach for characterization of hydrophobicity can be extended to artificial planar networks of other soft matter.
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588.|Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
Chongqin
C
Zhu
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588.
Yurui
Y
Gao
Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China.|Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Hui
H
Li
Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China.|Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.
Sheng
S
Meng
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588.
Lei
L
Li
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588; jfrancisco3@unl.edu xzeng1@unl.edu.
Joseph S
JS
Francisco
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588; jfrancisco3@unl.edu xzeng1@unl.edu.|Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
Xiao Cheng
XC
Zeng
D000596:Amino Acids / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D014867:Water
D000596:Amino Acids; D010455:Peptides; D014867:Water
amino acids; contact angle; hydrophobicity; nanodroplet; water