Theory and Simulation of Water Permeation in Aquaporin-1 |
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Authors: | Fangqiang Zhu Emad Tajkhorshid and Klaus Schulten |
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Institution: | Theoretical and Computational Biophysics Group, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 |
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Abstract: | We discuss the difference between osmotic permeability pf and diffusion permeability pd of single-file water channels and demonstrate that the pf/pd ratio corresponds to the number of effective steps a water molecule needs to take to permeate a channel. While pd can be directly obtained from equilibrium molecular dynamics simulations, pf can be best determined from simulations in which a chemical potential difference of water has been established on the two sides of the channel. In light of this, we suggest a method to induce in molecular dynamics simulations a hydrostatic pressure difference across the membrane, from which pf can be measured. Simulations using this method are performed on aquaporin-1 channels in a lipid bilayer, resulting in a calculated pf of 7.1 × 10−14 cm3/s, which is in close agreement with observation. Using a previously determined pd value, we conclude that pf/pd for aquaporin-1 measures ~12. This number is explained in terms of channel architecture and conduction mechanism. |
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