title: Identification of a Natural Green Light Absorbing Chloride Conducting Channelrhodopsin from Proteomonas sulcata.
abstract: Chloride conducting channelrhodopsins (ChloCs) are new members of the optogenetic toolbox that enable neuronal inhibition in target cells. Originally, ChloCs have been engineered from cation conducting channelrhodopsins (ChRs), and later identified in a cryptophyte alga genome. We noticed that the sequence of a previously described Proteomonas sulcata ChR (PsChR1) was highly homologous to the naturally occurring and previously reported ChloCs GtACR1/2, but was not recognized as an anion conducting channel. Based on electrophysiological measurements obtained under various ionic conditions, we concluded that the PsChR1 photocurrent at physiological conditions is strongly inward rectifying and predominantly carried by chloride. The maximum activation was noted at excitation with light of 540 nm. An initial spectroscopic characterization of purified protein revealed that the photocycle and the transport mechanism of PsChR1 differ significantly from cation conducting ChRs. Hence, we concluded that PsChR1 is an anion conducting ChR, now renamed PsACR1, with a red-shifted absorption suited for multicolor optogenetic experiments in combination with blue light absorbing cation conducting ChRs.
authors.affiliation: From the Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115 Berlin, Germany jonas.wietek@gmail.com.
authors.forename: Jonas
authors.identifier: http://orcid.org/0000-0002-8079-7042
authors.initials: J
authors.lastname: Wietek
authors.affiliation: From the Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Broser
authors.affiliation: From the Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115 Berlin, Germany.
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Krause
authors.affiliation: From the Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115 Berlin, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hegemann
mesh_terms: D018118:Chloride Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D044785:Cryptophyta / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D008027:Light; D012243:Rhodopsin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D018118:Chloride Channels; D012243:Rhodopsin
keywords: algae; biophysics; channelrhodopsin; chloride channel; electrophysiology; optogenetics; patch clamp; photobiology; ultraviolet-visible spectroscopy (UV-Vis spectroscopy)