Site-specific water dynamics in the first hydration layer of an anti-freeze glyco-protein: a simulation study

Antifreeze glycoproteins (AFGPs) inhibit ice recrystallization by a mechanism remaining largely elusive. The dynamics of AFGPs' hydration water and its involvement in the antifreeze activity, for instance, have not been identified conclusively. We herein, by simulation and theory, examined the picosecond site-specific water dynamics in the first hydration layer of a solvated AFGP8. Using a hydrogen bond switch event-based treatment, we strictly excluded the non-first layer water contribution. The observed water dynamics is much more retarded and inhomogeneous compared to the result of other commonly adopted treatments with non-first layer water contributions included. A molecular jump model analysis, with the cross-correlation between hydrogen bond switch molecular frames included, further indicates that excluding the non-first layer water contribution enhances the slow component in water dynamics, which couples strongly with the local environment. Further comparison with the structured ubiquitin protein revealed that, although the overall relaxation time distributions are similar between two proteins, a significant portion (>30%) of water hydrogen bond switching processes on the AFGP8 surface are considerably slower since they are trapped between the disaccharides and other protein regions. AFGP8 therefore resembles much the situation of an enzyme binding cleft or a DNA groove, where considerable slowdown of hydration water dynamics is observed due to the confinement. When bound to the ice surface, these slow, disordered water molecules may become a factor hindering the ice growth.