title: Theory and simulation of water permeation in aquaporin-1.
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 x 10(-14) cm(3)/s, which is in close agreement with observation. Using a previously determined pd value, we conclude that pf/pd for aquaporin-1 measures approximately 12. This number is explained in terms of channel architecture and conduction mechanism.
authors.affiliation: Theoretical and Computational Biophysics Group, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Fangqiang
authors.initials: F
authors.lastname: Zhu
authors.forename: Emad
authors.initials: E
authors.lastname: Tajkhorshid
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
mesh_terms: D051398:Aquaporin 1; D020346:Aquaporins / Q000737:chemistry*; D001665:Binding Sites; D003198:Computer Simulation; D004058:Diffusion; D008051:Lipid Bilayers / Q000737:chemistry*; D046911:Macromolecular Substances; D008956:Models, Chemical; D008958:Models, Molecular; D009997:Osmotic Pressure; D010539:Permeability; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D014867:Water / Q000737:chemistry*
chemical_list: D020346:Aquaporins; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D010714:Phosphatidylethanolamines; D014867:Water; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine; D051398:Aquaporin 1