Water is the enviroment that the polypeptide chain exists in, interacts with, and responds to.
The native structure of a protein is the direct result of the interaction of the polypeptide chain with water. The general distribution of side chains within the three-dimensional structure of globular proteins appears to be the direct consequence of being in the water environment. Chemical characteristics of water Water is pretty unique stuff. I seem to have digressed a bit. As a result of these characteristics, water molecules are polar and can participate in hydrogen bonding interactions.