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Imaging the Electrostatic Potential of Transmembrane Channels: Atomic Probe Microscopy of OmpF Porin
Philippsen, Ansgar Engel, Andreas Schirmer, Tilman Roux, Benoît Müller, Daniel J. Im, Wonpil
Philippsen, Ansgar
Engel, Andreas
Schirmer, Tilman
Roux, Benoît
Müller, Daniel J.
Im, Wonpil
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Abstract
The atomic force microscope (AFM) was used to image native OmpF porin and to detect the electrostatic potential generated by the protein. To this end the OmpF porin trimers from Escherichia coli was reproducibly imaged at a lateral resolution of ∼0.5 nm and a vertical resolution of ∼0.1 nm at variable electrolyte concentrations of the buffer solution. At low electrolyte concentrations the charged AFM probe not only contoured structural details of the membrane protein surface but also interacted with local electrostatic potentials. Differences measured between topographs recorded at variable ionic strength allowed mapping of the electrostatic potential of OmpF porin. The potential map acquired by AFM showed qualitative agreement with continuum electrostatic calculations based on the atomic OmpF porin embedded in a lipid bilayer at the same electrolyte concentrations. Numerical simulations of the experimental conditions showed the measurements to be reproduced quantitatively when the AFM probe was included in the calculations. This method opens a novel avenue to determine the electrostatic potential of native protein surfaces at a lateral resolution better than 1 nm and a vertical resolution of ∼0.1 nm.
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This is the published version. Copyright 2002 by Elsevier.
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2002-03
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Elsevier
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Philippsen, Ansgar, Wonpil Im, Andreas Engel, Tilman Schirmer, Benoit Roux, and Daniel J. Müller. "Imaging the Electrostatic Potential of Transmembrane Channels: Atomic Probe Microscopy of OmpF Porin." Biophysical Journal 82.3 (2002): 1667-676. http://dx.doi.org/10.1016/S0006-3495(02)75517-3.