Water Serves As A Protein Glue

Water forms an adhesive hydrogen-bond network in the interface between hydrophilic protein surfaces, suggests a group led by Volkhard Helms of Saarland University, in Germany (Nat. Commun., DOI: 10.1038/ncomms1258). Hydrophilic protein interactions are not as well studied as hydrophobic protein-protein interactions, in which water molecules are typically excluded from the interface. To learn more, Helms and colleagues turned to a computer model to determine the association between the hydrophilic surfaces of barnase, a bacterial ribonuclease, and its inhibitor protein, barstar. They found that water bridges form between protein residues as the two molecules come together. These bridges stabilize the proteins’ initial interactions and guide them together. Water between the proteins also has a reduced dielectric constant compared with bulk water, a characteristic that appears to enhance electrostatic interactions between the proteins, the researchers note. Water continues to play an adhesive role once the proteins are docked, with the known crystal structure of the complex showing nine water molecules that may mediate hydrogen bonds between the proteins, in addition to direct contacts between amino acids.