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Biophys. J. BioFAST: First Published November 18, 2005. doi:10.1529/biophysj.105.072298
© 2005 by the Biophysical Society.

A more recent version of this article appeared on February 15, 2006.
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CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING

CHEMICAL MODIFICATION OF THE BACTERIAL PORIN OMPF: GAIN OF SELECTIVITY BY VOLUME REDUCTION

Maarten Vrouenraets 1, Jenny Wierenga 1, Wim Meijberg 1 and Henk Miedema 1*

1 Biomade Technology Foundation

* To whom correspondence should be addressed. E-mail: miedema{at}biomade.nl.

Submitted on August 9, 2005
Revised on September 20, 2005
Accepted on 2 November 2005


  Abstract
OmpF is an essentially non-selective porin isolated from the outer membrane of Escherichia coli. Here we report on the manipulation of the ion selectivity of OmpF by chemical modification with the MTS reagents (MTSET, MTSEA and MTSES) and the (rather bulky) tripeptide glutathione, all cysteine-specific. When recorded in a gradient of 0.1//1 M CaCl2 or 0.1//1 M NaCl, pH 7.4 solutions, measured reversal potentials of the most cation-selective modified mutants were (virtually) identical to the Nernst potential of Ca2+ or Na+. Compared to this full cation selectivity, the anion-selective modified mutants performed somewhat less but nevertheless showed high anion selectivity. We conclude that a low permanent charge in combination with a narrow pore can render the same selectivity as a highly charged but wider pore. These results favor the view that both the electrostatic potential arising form the fixed charge in the pore and the space available at the selectivity filter contribute to the charge selection (i.e, cation versus anion selectivity) of a biological ion channel.

Key Words: Filter volume, Glutathione, Ion selectivity, MTS-reagents, OmpF, Porin




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Copyright © 2005 by the Biophysical Society.