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Biophys. J. BioFAST: First Published January 6, 2006. doi:10.1529/biophysj.105.073965
© 2006 by the Biophysical Society.

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BIOPHYSICAL THEORY AND MODELING

Single-channel Water Permeabilities of E.coli Aquaporins AqpZ and GlpF

Morten O Jensen 1 and Ole G. Mouritsen 2*

1 Univ. of Southern Denmark
2 MEMPHYS Center for Biomembrane Physics

* To whom correspondence should be addressed. E-mail: ogm{at}memphys.sdu.dk.

Submitted on September 6, 2005
Revised on October 13, 2005
Accepted on 12 December 2005


  Abstract
From equilibrium molecular dynamics simulations we have determined single channel water permeabilities for E.coli aquaporin Z (AqpZ) and aquaglyceroporin GlpF with the channels embedded in lipid bilayers. GlpF's osmotic water permeability constant pf exceed by two to three times that of AqpZ and the diffusive permeability constant (pd) of GlpF is found to exceed that of AqpZ two to nine 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{approx} 12 is close to the average number of water molecules in the channel lumen while for GlpF pf/pd{approx} 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 suppresses 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.

Key Words: aquaporin, channel radius, electrostatics, molecular dynamics, water channel, water permeability




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Copyright © 2006 by the Biophysical Society.