Hierarchy of Motions and Quasi-Particles in a Simplified Model of Potassium Channel Selectivity Filter

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We develop a simplified model of the multiply occupied Kcsa-like selectivity filter based on the best available structural data. The existence of hierarchy of motions in the selectivity filter is shown. Fast fluctuations of the ion-ion distances may be considered adiabatically decoupled from the slow diffusive motion of the ions' center of masses. The latter can be considered as a quasi-particle, called a quasi-ion, moving in an effective potential. In the Kcsa-like selectivity filter occupied by three ions the effective potential allows free barrier-less diffusional motion of the quasi-ions. The concept of the quasi-ions performing ion translocation through the channel may be vital in explaining barrier-less ‘knock-on’ conduction postulated for real channels.

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