Protein Surface Dynamics: Interaction with Water and Small Solutes |
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Authors: | Ran Friedman Esther Nachliel Menachem Gutman |
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Institution: | (1) Laser Laboratory for Fast Reactions in Biology, Department of Biochemistry, The George S. Wise Faculty for Life Sciences, Tel Aviv University, Tel Aviv, Israel |
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Abstract: | Previous time resolved measurements had indicated that protons could propagate on the surface of a protein, or a membrane,
by a special mechanism that enhances the shuttle of the proton towards a specific site 1]. It was proposed that a proper
location of residues on the surface contributes to the proton shuttling function. In the present study, this notion was further
investigated using molecular dynamics, with only the mobile charge replaced by Na+ and Cl− ions. A molecular dynamics simulation of a small globular protein (the S6 of the bacterial ribosome) was carried out in the
presence of explicit water molecules and four pairs of Na+ and Cl− ions. A 10 ns simulation indicated that the ions and the protein's surface were in equilibrium, with rapid passage of the
ions between the protein's surface and the bulk. Yet it was noted that, close to some domains, the ions extended their duration
near the surface, suggesting that the local electrostatic potential prevented them from diffusing to the bulk. During the
time frame in which the ions were detained next to the surface, they could rapidly shuttle between various attractor sites
located under the electrostatic umbrella. Statistical analysis of molecular dynamics and electrostatic potential/entropy consideration
indicated that the detainment state is an energetic compromise between attractive forces and entropy of dilution. The similarity
between the motion of free ions next to a protein and the proton transfer on the protein's surface are discussed. |
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Keywords: | molecular dynamics ions at interface protein-salt interactions |
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