Energy fluctuations in water: How are they coupled to protein dynamics and vice versa?

The exotic properties of water have intrigued researchers over a long time. Aqueous solutions of complex biomolecules like proteins trigger further interest. Several theories address the complexity of protein-water interactions. Frauenfelder et al. hypothesized the solvent slaving of protein dynamics. In this work, for the first time, we propose a mechanistic pathway of such protein-water coupling. Using atomistic molecular dynamics simulations on five proteins, we find that water dipoles efficiently interact with polar groups at the protein core. The forces thus experienced are comparable to the forces of interaction with other protein atoms. We also find that the fluctuations in self-energy of protein are significantly anti-correlated to the fluctuations in protein-water interaction energy. This signifies a microscopic channel of energy flow between protein and water. This coupling is also manifested in the total energy spectrum of protein which shows bimodal 1/f noise characteristics. The additional slope in the spectrum shows signature of perturbation from water as shown by Ohmine et al.

S. Mukherjee, S. Mondal, B. Bagchi Phys. Rev. Lett. (Under review)
Frauenfelder et al. Proc. Natl. Acad. Sci. U.S.A. 106, 5129 (2009)
Ohmine et al. Chem. Rev. 93, 2545 (1993)