Diversity and molecular mechanisms of channelrhodopsins.

Abstract

Channelrhodopsins (ChRs) are light-gated channels that guide phototaxis in eukaryotic microorganisms and are widely used as molecular tools to control cell membrane potential with light (optogenetics). Expression of ChR genes in neurons and cardiomyocytes enables photoactivation or photoinhibition of these cells’ activity with submillisecond precision. Recent advances in polynucleotide sequencing have led to identification of hundreds of ChR homologs in many phylogenetic lineages, but only a few have been characterized functionally. ChRs differ in their ionic selectivity, spectral sensitivity, and photocurrent kinetics and thus provide an exceptional platform for the study of structure-function relationships in membrane proteins. Current evidence suggests that ion channel function has evolved within the superfamily of microbial rhodopsins by several convergent routes. Our laboratory has discovered natural ChR variant families with major different biophysical properties, and we are studying their photochemical mechanisms by atomic structure determination, electrophysiology, kinetic spectroscopy, and structure/function analysis by mutagenesis. Also, we apply molecular engineering to improve their biophysical properties to suit practical needs of optogenetics. Recently we identified potassium-selective ChRs in non-photosynthetic stramenopile and alveolate microbes and demonstrated the utility of these molecules as inhibitory optogenetic tools. These proteins are promising for research and potentially for treatment of potassium channelopathies such as epilepsy, Parkinson's disease, and cardiac arrhythmias.