Anion-conducting channelrhodopsin

iChloC structure
Figure 1: It took 5 point mutations to create iChloC from cation-conducting Channelrhodopsin-2.[1]

Anion-conducting channelrhodopsins are light-gated ion channels that open in response to light and let negatively charged ions (such as chloride) enter a cell. All channelrhodopsins use retinal as light-sensitive pigment, but they differ in their ion selectivity. Anion-conducting channelrhodopsins are used as tools to manipulate brain activity in mice, fruit flies and other model organisms (Optogenetics). Neurons expressing anion-conducting channelrhodopsins are silenced when illuminated with light, an effect that has been used to investigate information processing in the brain. For example, suppressing dendritic calcium spikes in specific neurons with light reduced the ability of mice to perceive a light touch to a whisker.[2] Studying how the behavior of an animal changes when specific neurons are silenced allows scientists to determine the role of these neurons in the complex circuits controlling behavior.

The first anion-conducting channelrhodopsins were engineered from the cation-conducting light-gated channel Channelrhodopsin-2 by removing negatively charged amino acids from the channel pore (Fig. 1).[3] As the main anion of extracellular fluid is chloride (Cl−), anion-conducting channelrhodopsins are also known as “chloride-conducting channelrhodopsins” (ChloCs). Naturally occurring anion-conducting channelrhodopsins (ACRs) were subsequently identified in cryptophyte algae.[4][5][6] The crystal structure of the natural GtACR1 has recently been solved, paving the way for further protein engineering.[7][8]

Structure of bromide-bound GtACR1 (PDB: 7LE1). The two gray planes indicate the hydrocarbon boundaries of the lipid bilayer and were calculated with the ANVIL algorithm.[9]
  1. ^ Cite error: The named reference Wietek2015 was invoked but never defined (see the help page).
  2. ^ Takahashi, Naoya; Oertner, Thomas G.; Hegemann, Peter; Larkum, Matthew E. (2016-12-23). "Active cortical dendrites modulate perception". Science. 354 (6319): 1587–1590. Bibcode:2016Sci...354.1587T. doi:10.1126/science.aah6066. ISSN 0036-8075. PMID 28008068. S2CID 28317052.
  3. ^ Wietek, Jonas; Wiegert, J. Simon; Adeishvili, Nona; Schneider, Franziska; Watanabe, Hiroshi; Tsunoda, Satoshi P.; Vogt, Arend; Elstner, Marcus; Oertner, Thomas G.; Hegemann, Peter (2014-04-25). "Conversion of Channelrhodopsin into a Light-Gated Chloride Channel". Science. 344 (6182): 409–412. Bibcode:2014Sci...344..409W. doi:10.1126/science.1249375. ISSN 0036-8075. PMID 24674867. S2CID 206554245.
  4. ^ Cite error: The named reference Govorunova2015 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference :1 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference :4 was invoked but never defined (see the help page).
  7. ^ Kato, Hideaki E.; Kim, Yoon Seok; Paggi, Joseph M.; Evans, Kathryn E.; Allen, William E.; Richardson, Claire; Inoue, Keiichi; Ito, Shota; Ramakrishnan, Charu (2018-08-29). "Structural mechanisms of selectivity and gating in anion channelrhodopsins". Nature. 561 (7723): 349–354. Bibcode:2018Natur.561..349K. doi:10.1038/s41586-018-0504-5. ISSN 0028-0836. PMC 6317992. PMID 30158697.
  8. ^ Kim, Yoon Seok; Kato, Hideaki E.; Yamashita, Keitaro; Ito, Shota; Inoue, Keiichi; Ramakrishnan, Charu; Fenno, Lief E.; Evans, Kathryn E.; Paggi, Joseph M. (2018-08-29). "Crystal structure of the natural anion-conducting channelrhodopsin GtACR1". Nature. 561 (7723): 343–348. Bibcode:2018Natur.561..343K. doi:10.1038/s41586-018-0511-6. ISSN 0028-0836. PMC 6340299. PMID 30158696.
  9. ^ Postic, Guillaume; Ghouzam, Yassine; Guiraud, Vincent; Gelly, Jean-Christophe (2016). "Membrane positioning for high- and low-resolution protein structures through a binary classification approach". Protein Engineering, Design and Selection. 29 (3): 87–91. doi:10.1093/protein/gzv063. PMID 26685702.