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Ionic interactions in multiply occupied channels.

V L Dorman¹, S Garofoli, P C Jordan

¹Department of Chemistry, Brandeis University, Waltham, MA 02454-9110, USA.

Novartis Foundation Symposium

|September 3, 1999

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Understanding ion channel function requires analyzing multi-ion mechanisms. This study reveals how ion-water-peptide interactions influence ion permeation energetics in channels like gramicidin A and KcsA K+.

Area of Science:

Biophysics
Computational Biology
Structural Biology

Background:

Many ion channels utilize multi-ion mechanisms for physiological function.
Ion-ion repulsion is crucial for ion permeation through these channels.
Understanding these interactions is key to explaining channel selectivity and transport.

Purpose of the Study:

To investigate the energetic consequences of multiple ion occupancy in ion channels.
To analyze the role of ion-water and ion-peptide correlations in ion permeation.
To compare these effects in idealized models of gramicidin A and KcsA K+ channels.

Main Methods:

Application of the semi-microscopic Monte Carlo approach.
Analysis of excess repulsion energy, accounting for ion-water and ion-peptide correlations.

Related Experiment Videos

Modeling of double occupancy in gramicidin A and KcsA K+ channel systems.

Main Results:

In gramicidin, pair occupancy is influenced by bulk solvent, channel water, and peptide backbone interactions.
In KcsA, uneven spacing and large ion-water distances in the selectivity filter promote double occupancy.
Channel binding pocket design in KcsA reduces net ionic repulsion compared to gramicidin-like structures.

Conclusions:

Ion-water-peptide correlations significantly impact ion permeation energetics in multi-ion channels.
The structural features of the KcsA channel's selectivity filter and binding sites are optimized to modulate ion repulsion.
These findings provide insights into the molecular mechanisms governing ion transport through biological channels.