Current Fluctuation Analysis in a Protein Nanopore

Abstract

Current fluctuation analysis has been widely used over the recent years to study the kinetic effects of different biological systems like neuronal networks or biomembranes. In particular, noise analysis has been successfully employed in protein ion channels to investigate the transport mechanisms that control the channel function. In this work, current fluctuations are analyzed in a protein nanopore, OmpF from E. coli. The study is performed for different electrolytes, including KCl, LiCl, MgCl2, and CaCl2, over a wide range of concentrations and voltages. Previous studies addressing current fluctuations in OmpF investigated the pH titration of the channel residues by analyzing the Lorentzian-like shape of the power spectral densities [1]. A complementary approach is followed here, based on the noise studies of Hoogerheide and colleagues in synthetic nanopores [2]. Special attention is paid to the additional white noise seen in the low frequency range of the power spectral density. The average noise scales with the square of the dc current, showing that this frequency−independent excess noise originates from conductance fluctuations. These fluctuations are analyzed here in terms of the ionic concentration to disclose the different transport mechanisms occurring in OmpF channel.[1] E.M. Nestorovich et al. (2003) Biophys. J. 85:3718−3729[2] D.P. Hoogerheide et al. (2009) Phys. Rev. Lett. 102:256804