Abstract
Channelrhodopsin-2 (ChR2) is an important tool for optogenetics, and some of its mutants are Ca2+-selective channels. However, the mechanism for Ca2+-selective permeation is still unclear. In this study, molecular dynamic (MD) simulations for the Ca2+ permeation of the CatCh mutant were carried out to investigate the fundamental features of the selectivity of Ca2+. Research on the conformational changes in the key residues near the central gate (CG) of the channel suggested that E83, E90, and D253 play an important role in Ca2+ conductivity. The clustering analysis indicates that the above “EED triad” acts as a filter, and Ca2+ can only pass through if the EED is in a certain conformation. It was also found that hydrated Ca2+ can be coordinated with carboxyl groups, resulting in the loss of part of the water molecules in the hydrated shell and a reduction in ionic radius, which helps Ca2+ enter the channel.