Influence of secondary structure on the hydration of serine, threonine and tyrosine residues in proteins.

Previous analysis of experimental data on the solvation of high resolution protein structures has shown that preferred interaction sites for water molecules exist around most amino acid side chains. We have extended this analysis to look in more detail at the distributions around serine, threonine and tyrosine. We find that for serine and threonine side chains the preferred interaction sites of solvent molecules with the hydroxyl group depends on secondary structure and the chi 1 torsion angle of the side chain. For tyrosine side chains the hydroxyl group is too far from the main chain to reflect secondary structure influences. Specific patterns of hydration are observed in which water molecules 'bridge' between the hydroxyl side-chain atom and another main chain or side-chain atom.