INFLUENCE OF A CHANNEL-FORMING PEPTIDE ON ENERGY BARRIERS TO ION PERMEATION, VIEWED FROM A CONTINUUM DIELECTRIC PERSPECTIVE

Citation
Mb. Partenskii et al., INFLUENCE OF A CHANNEL-FORMING PEPTIDE ON ENERGY BARRIERS TO ION PERMEATION, VIEWED FROM A CONTINUUM DIELECTRIC PERSPECTIVE, Biophysical journal, 67(4), 1994, pp. 1429-1438
Citations number
32
Categorie Soggetti
Biophysics
Journal title
ISSN journal
00063495
Volume
67
Issue
4
Year of publication
1994
Pages
1429 - 1438
Database
ISI
SICI code
0006-3495(1994)67:4<1429:IOACPO>2.0.ZU;2-E
Abstract
The continuum three-dielectric model for an aqueous ion channel pore-f orming peptide-membrane system is extended to account for the finite l ength of the channel. We focus on the electrostatic influence that a c hannel-forming peptide may exert on energy barriers to ion permeation. The nonlinear dielectric behavior of chan nel water caused by dielect ric saturation in the presence of an ion is explicitly modeled by assi gning channel water a mean dielectric constant much less than that of bulk water. An exact solution of the continuum problem is formulated b y approximating the dielectric behavior of bulk water, assigning it a dielectric constant of infinity. The validity of this approximation is verified by comparison with a Poisson-Boltzmann description of the el ectrolyte. The formal equivalence of high ionic strength and high elec trolyte dielectric constant is demonstrated. We estimate limits on the reduction of the electrostatic free energy caused by ionic interactio n with the channel-forming peptide. We find that even assigning this r egion an epsilon of 100, its influence is insufficient to lower permea tion free energy barriers to values consistent with observed channel c onductances. We provide estimates of the effective dielectric constant of this highly polarizable region, by comparing energy barriers compu ted using the continuum approach with those found from a semimicroscop ic analysis of a simplified model of a gramicidin-like charge distribu tion. Possible ways of improving both models are discussed.