Water dynamics on the surface of the protein barstar

Abstract

Water plays a fundamental function in life and technology. To gain a deeper knowledge to the problem of the hydration of biomolecules, the dynamics of water around an 89-residue protein of interest in molecular recognition, cancer cell research and amyloid fibrils investigations is analyzed. The biomolecule is the ribonuclease inhibitor barstar wild-type. The dynamics of the protein and the 7430 water molecules of the bath in which it is immersed is monitored during a period of 7 ns by using all-atom molecular dynamics simulations. The results confirm the existence of multiple time scales in the dynamics of water (10⁻¹ to 10³ ps) at the atomic level. That heterogeneity of residence times is not lost if the system of reference is just one atom of the inhibitor. The dehydration process of barstar is considered through the analysis of time correlation functions, obtaining an averaged decay time of τ = 84.0 ± 0.3 ps. A power law distribution, with scaling exponent α = 0.57 ± 0.04, suggests that this hydration water exhibits a scale free dynamics (with respect to the residence time of solvent molecules). Most of the water molecules located on the surface of the protein spend times smaller than the picosecond while only about 1% of them stay for periods of time on the nanosecond scale.