Evaluating long-range orientational ordering of water around proteins: Signature of a tug-of-war scenario

Long-range perturbations of water structure and dynamics by the biomolecules are subject of great interests due to their potential role in biomolecular recognition. In this article, we examine the local and long-range orientational structure of water molecules surrounding the proteins with different total charges (+8, 0 and -8) both with and without the presence of physiological salt environment. A prominent population of In-oriented water molecules is observed at the first hydration shell of the proteins, irrespective of their total charges. Starting from third hydration layer, water molecules report mainly the total charge of the respective protein. This long-range ordering persists up to even ninth hydration layer without physiological salt environment and vanishes beyond the fifth hydration shell at physiological salt environment. Long-range orientational orderings around different types of surface atoms of a protein show particularly rich and heterogeneous behaviours. When the surface atom’s charge and protein’s total charge are opposite, a clear signature of tug-of-war is demonstrated in the long-range orientational ordering of water molecules. While the water reports surface atom’s charge at lower distances, water molecules at longer distances reports total charge of the protein with a crossover around 10 Å. This phenomena persist even in the presence of physiological salt environment. The evidence of destructive/constructive superposition of water-mediated orientation waves originating from two individual proteins with similar/opposite total charges is also demonstrated here. These results are important in entangling long-range water-mediated recognition phenomena among biomolecules (protein-protein, protein-ligand, protein-DNA, etc).