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Biophysical Journal 86:50-57 (2004)
© 2004 The Biophysical Society

Theory and Simulation of Water Permeation in Aquaporin-1

Fangqiang Zhu, Emad Tajkhorshid and Klaus Schulten

Theoretical and Computational Biophysics Group, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Correspondence: Address reprint requests to Klaus Schulten, 405 N. Mathews, Urbana, IL 61801. Tel.: 217-244-1604; Fax: 217-244-6078; E-mail: kschulte{at}ks.uiuc.edu.

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 x 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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