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BIOPHYSICS
Electroosmotic enhancement of the binding of a neutral molecule to a transmembrane pore

Li-Qun Gu ^*, Stephen Cheley ^*, and Hagan Bayley ^*  

^*Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, TX 77843-1114; and Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom

Edited by Arthur Karlin, Columbia University College of Physicians and Surgeons, New York, NY, and approved October 22, 2003 (received for review March 27, 2003)

The flux of solvent water coupled to the transit of ions through protein pores is considerable. The effect of this electroosmotic solvent flow on the binding of a neutral molecule [-cyclodextrin (CD)] to sites within the staphylococcal -hemolysin pore was investigated. Mutant -hemolysin pores were used to which CD can bind from either entrance and through which the direction of water flow can be controlled by choosing the charge selectivity of the pore and the polarity of the applied potential. The K_d values for CD for individual mutant pores varied by >100-fold with the applied potential over a range of –120 to +120 mV. In all cases, the signs of the changes in binding free energy and the influence of potential on the association and dissociation rate constants for CD were consistent with an electroosmotic effect.

Abbreviations: HL, staphylococcal -hemolysin; CD, -cyclodextrin; EDL, electrical double layer; PEG, polyethylene glycol.

To whom correspondence should be addressed at: Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, England. E-mail: bayley{at}tamu.edu.

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