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J. Summhammer, G. Sulyok, G. Bernroider:
"Quantum Mechanical Coherence of K+ Ion Wave Packets Increases Conduction in the KcsA Ion Channel";
Applied Sciences, 2020 (2020), 10.

We simulate the transmission of K + ions through the KcsA potassium ion channel filter
region at physiological temperatures, employing classical molecular dynamics (MD) at the atomic
scale together with a quantum mechanical version of MD simulation (QMD), treating single ions
as quantum wave packets. We provide a direct comparison between both concepts, embedding the
simulations into identical force fields and thermal fluctuations. The quantum simulations permit
the estimation of coherence times and wave packet dispersions of a K + ion over a range of 0.5 nm
(a range that covers almost 50% of the filter domains longitudinal extension). We find that this
observed extension of particle delocalization changes the mean orientation of the coordinating
carbonyl oxygen atoms significantly, transiently suppressing their `caging action´ responsible for
selective ion coordination. Compared to classical MD simulations, this particular quantum effect
allows the K + ions to `escape´ more easily from temporary binding sites provided by the surrounding
filter atoms. To further elucidate the role of this observation for ion conduction rates, we compare the
temporal pattern of single conduction events between classical MD and quantum QMD simulations
at a femto-sec time scale. A finding from both approaches is that ion permeation follows a very
irregular time pattern, involving flushes of permeation interrupted by non-conductive time intervals.
However, as compared with classical behavior, the QMD simulation shortens non-conductive time by
more than a half. As a consequence, and given the same force-fields, the QMD-simulated ion current
appears to be considerably stronger as compared with the classical current. To bring this result in
line with experimentally observed ion currents and the predictions based on Nernst-Planck theories,
the conclusion is that a transient short time quantum behavior of permeating ions can successfully
compromise high conduction rates with ion selectivity in the filter of channel proteins.

potassium ion channel; KcsA channel; selectivity filter; quantum wave packet; coherence time; biological quantum coherence

http://dx.doi.org/10.3390/app10124250

https://publik.tuwien.ac.at/files/publik_293354.pdf