dorsal/arxiv
View SchemaTuning ion coordination preferences to enable selective permeation
| Authors | Sameer Varma, Susan B. Rempe |
|---|---|
| Categories | |
| ArXiv ID | physics/0608180 |
| URL | https://arxiv.org/abs/physics/0608180 |
| DOI | 10.1529/biophysj.107.107482 |
Abstract
Potassium (K-) channels catalyze K+ ion permeation across cellular membranes while simultaneously discriminating their permeation over Na+ ions by more than a factor of a thousand. Structural studies show bare K+ ions occupying the narrowest channel regions in a state of high coordination by all 8 surrounding oxygen ligands from the channel walls. As in most channels, the driving force for selectivity occurs when one ion is preferentially stabilized or destabilized by the channel compared to water. In the common view of mechanism, made vivid by textbook graphics, the driving force for selectivity in K- channels arises by a fit, whereby the channel induces K+ ions to leave water by offering an environment like water for K+, in terms of both energy and local structure. The implication that knowledge of local ion coordination in a liquid environment translates to design parameters in a protein ion channel, producing similar energetic stabilities, has gone unchallenged, presumably due in part to lack of consensus regarding ion coordination structures in liquid water. Growing evidence that smaller numbers and different arrangements of ligands coordinate K+ ions in liquid water, however, raises new questions regarding mechanism: how and why should ion coordination preferences change, and how does that alter the current notions of ion selectivity? Our studies lead to a new channelcentric paradigm for the mechanism of K+ ion channel selectivity. Because the channel environment is not liquid-like, the channel necessarily induces local structural changes in ion coordination preferences that enable structural and energetic differentiation between ions.
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"abstract": "Potassium (K-) channels catalyze K+ ion permeation across cellular membranes\nwhile simultaneously discriminating their permeation over Na+ ions by more than\na factor of a thousand. Structural studies show bare K+ ions occupying the\nnarrowest channel regions in a state of high coordination by all 8 surrounding\noxygen ligands from the channel walls. As in most channels, the driving force\nfor selectivity occurs when one ion is preferentially stabilized or\ndestabilized by the channel compared to water. In the common view of mechanism,\nmade vivid by textbook graphics, the driving force for selectivity in K-\nchannels arises by a fit, whereby the channel induces K+ ions to leave water by\noffering an environment like water for K+, in terms of both energy and local\nstructure. The implication that knowledge of local ion coordination in a liquid\nenvironment translates to design parameters in a protein ion channel, producing\nsimilar energetic stabilities, has gone unchallenged, presumably due in part to\nlack of consensus regarding ion coordination structures in liquid water.\nGrowing evidence that smaller numbers and different arrangements of ligands\ncoordinate K+ ions in liquid water, however, raises new questions regarding\nmechanism: how and why should ion coordination preferences change, and how does\nthat alter the current notions of ion selectivity? Our studies lead to a new\nchannelcentric paradigm for the mechanism of K+ ion channel selectivity.\nBecause the channel environment is not liquid-like, the channel necessarily\ninduces local structural changes in ion coordination preferences that enable\nstructural and energetic differentiation between ions.",
"arxiv_id": "physics/0608180",
"authors": [
"Sameer Varma",
"Susan B. Rempe"
],
"categories": [
"physics.bio-ph"
],
"doi": "10.1529/biophysj.107.107482",
"title": "Tuning ion coordination preferences to enable selective permeation",
"url": "https://arxiv.org/abs/physics/0608180"
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