The Ca2+ permeation mechanism of the ryanodine receptor revealed by a multi-site ion model
Aihua Zhang, Hua Yu, Chunhong Liu, Chen Song
Abstract
Abstract Ryanodine receptors (RyR) are ion channels responsible for the release of Ca 2+ from the sarco/endoplasmic reticulum and play a crucial role in the precise control of Ca 2+ concentration in the cytosol. The detailed permeation mechanism of Ca 2+ through RyR is still elusive. By using molecular dynamics simulations with a specially designed Ca 2+ model, we show that multiple Ca 2+ ions accumulate in the upper selectivity filter of RyR1, but only one Ca 2+ can occupy and translocate in the narrow pore at a time, assisted by electrostatic repulsion from the Ca 2+ within the upper selectivity filter. The Ca 2+ is nearly fully hydrated with the first solvation shell intact during the whole permeation process. These results suggest a remote knock-on permeation mechanism and one-at-a-time occupation pattern for the hydrated Ca 2+ within the narrow pore, uncovering the basis underlying the high permeability and low selectivity of the RyR channels.