title: Single-channel water permeabilities of Escherichia coli aquaporins AqpZ and GlpF.
abstract: From equilibrium molecular dynamics simulations we have determined single-channel water permeabilities for Escherichia coli aquaporin Z (AqpZ) and aquaglyceroporin GlpF with the channels embedded in lipid bilayers. GlpF's osmotic water permeability constant pf exceeds by 2-3 times that of AqpZ and the diffusive permeability constant (pd) of GlpF is found to exceed that of AqpZ 2-9-fold. Achieving complete water selectivity in AqpZ consequently implies lower transport rates overall relative to the less selective, wider channel of GlpF. For AqpZ, the ratio pf/pd congruent with 12 is close to the average number of water molecules in the channel lumen, whereas for GlpF, pf/pd congruent with 4. This implies that single-file structure of the luminal water is more pronounced for AqpZ, the narrower channel of the two. Electrostatics profiles across the pore lumens reveal that AqpZ significantly reinforces water-channel interactions, and weaker water-water interactions in turn suppress water-water correlations relative to GlpF. Consequently, suppressed water-water correlations across the narrow selectivity filter become a key structural determinant for water permeation causing luminal water to permeate slower across AqpZ.
authors.affiliation: MEMPHYS-Center for Biomembrane Physics, Department of Physics, University of Southern Denmark, DK-5230 Odense M, Denmark.
authors.forename: Morten Ø
authors.initials: MØ
authors.lastname: Jensen
authors.forename: Ole G
authors.initials: OG
authors.lastname: Mouritsen
mesh_terms: D020346:Aquaporins / Q000378:metabolism / Q000502:physiology*; D001703:Biophysics / Q000379:methods*; D050260:Carbohydrate Metabolism; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D030562:Databases, Protein; D004058:Diffusion; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000502:physiology*; D006639:Histidine / Q000737:chemistry; D007700:Kinetics; D008051:Lipid Bilayers; D008565:Membrane Proteins / Q000502:physiology*; D008958:Models, Molecular; D015233:Models, Statistical; D008962:Models, Theoretical; D009995:Osmosis; D010539:Permeability; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D011522:Protons; D055672:Static Electricity; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D020346:Aquaporins; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D011522:Protons; C106425:aqpZ protein, E coli; D014867:Water; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine; C078043:GlpF protein, E coli; D006639:Histidine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine