Interaction between a twelve-residue segment of antifreeze protein type I,or its mutants,and water molecules

A molecular dynamics simulation has been carried out for water molecules with a rigid segment of antifreeze protein type I. The segment consists of nine alanine residues, two threonine residues and one asparagine residue. Mutant segments, in which the threonine residues are replaced with valine residues, or serine residues, are also used. It is predicted that the hydrogen site of asparagine residue, and that of threonine residue, play an important role in the hydrogen bond of water molecules in these sites. This hydrogen bond is not noticeable between water molecules and the valine residue, or serine residue. The existence of four hydrophilic sites enhances the mobility of water molecules close to the serine residue of the mutant segment. The difference in the zenith-angle fluctuations of the original segment and the valine-mutant segment is less noticeable in the case of 230 K. This is because the gathering of water molecules due to the hydrophobic hydration is predominant near the alanine residues of the segments at this temperature.