Hydration Mimicry by Membrane Ion Channels

TL;DR

This paper explores how ion channels in membranes may facilitate ion transport by mimicking the hydration environment of ions in water, emphasizing the importance of hydration structures and free energies.

Contribution

It reviews ion hydration structures and free energies, proposing new calculations and experiments to better understand hydration mimicry in membrane channels.

Findings

Hydration structures of ions in bulk water are characterized.

Molecular quasi-chemical theory provides hydration free energies.

Suggestions for further physical-chemical studies on ion-channel interactions.

Abstract

Ions transiting biomembranes might pass readily from water through ion-specific membrane proteins if those protein channels provide environments similar to the aqueous solution hydration environment. Indeed, bulk aqueous solution is an important reference condition for the ion permeation process. Assessment of this hydration mimicry view depends on understanding the hydration structure and free energies of metal ions in water to provide a comparison for the membrane channel environment. To refine these considerations, we review local hydration structures of ions in bulk water, and the molecular quasi-chemical theory that provides hydration free energies. In that process, we note some current views of ion-binding to membrane channels and suggest new physical-chemical calculations and experiments that might further clarify the hydration mimicry view.