A pH-tunable nanofluidic diode: electrochemical rectification in a reconstituted single ion channel.
We report pH-dependent electrochemical rectification in a protein ion channel (the bacterial porin OmpF) reconstituted on a planar phospholipid membrane. The measurements performed at single-channel level show that the electric current is controlled by the protein fixed charge and it can be tuned by adjusting the local pH. Under highly asymmetric pH conditions, the channel behaves like a liquid diode. Unlike other nanofluidic devices that display also asymmetric conductance, here the microscopic charge distribution of the system can be explored by using the available high-resolution (2.4 A) channel crystallographic structure. Continuum electrostatics calculations confirm the hypothesized bipolar structure of the system. The selective titration of the channel residues is identified as the underlying physicochemical mechanism responsible for current rectification.
Alcaraz
Antonio
A
Department of Experimental Sciences, Biophysics Unit, University Jaume I, P.O. Box 8029, E-12080 Castellón, Spain.
Ramírez
Patricio
P
García-Giménez
Elena
E
López
M Lidón
ML
Andrio
Andreu
A
Aguilella
Vicente M
VM
D001426:Bacterial Proteins / Q000737:chemistry; D032701:Biomimetics; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels; D036103:Nanotechnology / Q000379:methods*; D018272:Porins / Q000737:chemistry*; D055672:Static Electricity
D001426:Bacterial Proteins; D007473:Ion Channels; C109237:OmpF protein; D018272:Porins