Residue ionization and ion transport through OmpF channels.
Single trimeric channels of the general bacterial porin, OmpF, were reconstituted into planar lipid membranes and their conductance, selectivity, and open-channel noise were studied over a wide range of proton concentrations. From pH 1 to pH 12, channel transport properties displayed three characteristic regimes. First, in acidic solutions, channel conductance is a strong function of pH; it increases by approximately threefold as the proton concentration decreases from pH 1 to pH 5. This rise in conductance is accompanied by a sharp increase in cation transport number and by pronounced open-channel low-frequency current noise with a peak at approximately pH 2.5. Random stepwise transients with amplitudes at approximately 1/5 of the monomer conductance are major contributors to this noise. Second, over the middle range (pH 5/pH 9), channel conductance and selectivity stay virtually constant; open channel noise is at its minimum. Third, over the basic range (pH 9/pH 12), channel conductance and cation selectivity start to grow again with an onset of a higher frequency open-channel noise. We attribute these effects to the reversible protonation of channel residues whose pH-dependent charge influences transport by direct interactions with ions passing through the channel.
Nestorovich
Ekaterina M
EM
Laboratory of Physical and Structural Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-0924, USA.
Rostovtseva
Tatiana K
TK
Bezrukov
Sergey M
SM
D000838:Anions; D018407:Bacterial Physiological Phenomena; D001692:Biological Transport; D055592:Biophysical Phenomena; D001703:Biophysics; D002412:Cations; D004594:Electrophysiology; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008051:Lipid Bilayers / Q000737:chemistry; D018272:Porins / Q000737:chemistry* / Q000502:physiology; D011522:Protons; D012997:Solvents
D000838:Anions; D002412:Cations; D007477:Ions; D008051:Lipid Bilayers; C109237:OmpF protein; D018272:Porins; D011522:Protons; D012997:Solvents