Charge Delocalization in Proton Channels, II: The Synthetic LS2 Channel and Proton Selectivity

TitleCharge Delocalization in Proton Channels, II: The Synthetic LS2 Channel and Proton Selectivity
Publication TypeJournal Article
Year of Publication2007
AuthorsWu, Y, Ilan, B, Voth, GA
JournalBiophys J
KeywordsBiophysics/*methods Cations Electric Conductivity Electrons Hydrogen/chemistry Ion Channel Gating Ion Channels/*chemistry Models, Molecular Molecular Conformation Potassium/chemistry Protein Conformation Protons Reproducibility of Results Thermodynamics Water/chemistry

In this study, the minimalist synthetic LS2 channel is used as a prototype to examine the selectivity of protons over other cations. The free-energy profiles along the transport pathway of LS2 are calculated for three cation species: a realistic delocalized proton (including Grotthuss shuttling)–H(+), a classical (nonshuttling) hydronium–H(3)O(+), and a potassium cation–K(+). The overall barrier for K(+) is approximately twice as large as that for H(+), explaining the >100 times larger maximal ion conductance for the latter, in qualitative agreement with the experimental result. The profile for the classical hydronium is quantitatively intermediate between those of H(+) and K(+) and qualitatively more similar to that of H(+), for which the locations of the peaks are well correlated with the troughs of the pore radius profile. There is a strong correlation between the free-energy profiles and the very different characteristic hydration structures of the three cation species. This work suggests that the passage of various cations through ion channels cannot always be explained by simple electrostatic desolvation considerations.