Abstract
Channelrhodopsins (ChRs) are light-gated transmembrane cation channels which are widely used for optogenetic technology. Replacing glutamate located at the central gate of the ion channel with positively charged amino acid residues will reverse ion selectivity and allow anion conduction. The structures and properties of the ion channel, the transport of chloride, and potential of mean force (PMF) of the chimera protein (C1C2) and its mutants, EK-TC, ER-TC and iChloC, were investigated by molecular dynamics simulation. The results show that the five-fold mutation in E122Q-E129R-E140S-D195N-T198C (iChloC) increases the flexibility of the transmembrane channel protein better than the double mutations in EK-TC and ER-TC, and results in an expanded ion channel pore size and decreased steric resistance. The iChloC mutant was also found to have a higher affinity for chloride ions and, based on surface electrostatic potential analysis, provides a favorable electrostatic environment for anion conduction. The PMF free energy curves revealed that high affinity Cl− binding sites are generated near the central gate of the three mutant proteins. The energy barriers for the EK-TC and ER-TC were found to be much higher than that of iChloC. The results suggest that the transmembrane ion channel of iChloC protein is better at facilitating the capture and transport of chloride ions.
Highlights
Channelrhodopsins (ChRs) are non-selective, light-gated cation channels that act as photoreceptor in microalgae and are widely used to activate specific groups of neurons in the brain [1,2,3]
classical molecular dynamics (CMD) simulations were performed on wild-type C1C2 (C1C2-WT) and mutants mentioned
Since most of the negatively charged residues are derived from TM2, we suggest that the ionic through the ion channels of three mutants (Figure 5A), and further estimated the energy changes of ion conductance and selectivity of C1C2-WT are primarily determined by TM2
Summary
Channelrhodopsins (ChRs) are non-selective, light-gated cation channels that act as photoreceptor in microalgae and are widely used to activate specific groups of neurons in the brain [1,2,3]. The chromophores of ChRs, retinal molecules, undergo photo-induced trans-cis isomerization, which initiates the photocycle reaction and leads to the opening of ion channels [4,5,6,7]. ChRs can non-selectively conduct monovalent cations such as Na+ , K+ , H+ and divalent cations such as Ca2+. The cation flow into cell will cause depolarization of neuron and lead to an excited neural stimulation. For wild-type (WT) ChRs, some physiological studies, such as neural circuit, learning and memory, and movement disorders, cannot be carried out because of the relatively low ion conductivity. It is necessary to design and optimize mutants of
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