Conductance and selectivity fluctuations in D127 mutants of the bacterial porin OmpF |
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Authors: | Henk Miedema Maarten Vrouenraets Jenny Wierenga Bob Eisenberg Tilman Schirmer Arnaud Baslé Wim Meijberg |
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Institution: | (1) Biomade Technology Foundation, Nijenborgh 4, 9747 AG Groningen, The Netherlands;(2) Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 W. Harrison Street, Suite 1291, Chicago, IL 60612, USA;(3) Division of Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 CH Basel, Switzerland |
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Abstract: | A recent molecular dynamics study questioned the protonation state and physiological role of aspartate 127 (D127) of E. coli porin OmpF. To address that question we isolated two OmpF mutants with D127 either neutralized (D127N) or replaced by a positively
charged lysine (D127K). The charge state of the residue at position 127 has clear effects on both conductance and selectivity.
The D127K but not the D127N mutant expresses resilient conductance and selectivity fluctuations. These fluctuations reflect,
we think, either changes in the ionization state of K127 and/or transitions between unstable subconformations as induced by
the electrostatic repulsion between two positively charged residues, K127 and the nearby R167. Our results slightly favor
the view that in WT OmpF residue D127 is deprotonated. As for the role of D127 in OmpF functionality, the gating of both mutants
shows very similar sensitivity toward voltage as WT OmpF. Moreover, the current fluctuations of the D127K mutant were observed
also in the absence of an applied electric field. We therefore dismiss D127 as a key residue in the control mechanism of the
voltage-dependent gating of OmpF. |
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Keywords: | Current fluctuations OmpF D127 mutant Ion selectivity OmpF Loop L3 |
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