Oral Presentation 2014 International Biophysics Congress

Channelrhodopsin et al.: Photoreceptors for optogenetic applications (#39)

Georg Nagel 1
  1. University of Würzburg, Würzburg, Germany

Several photoreceptors from microbes were molecularly identified and new ones are discovered, especially by genome mining. We could show that some of these photoreceptors are ideal tools to manipulate animal cells by illumination. We discovered the Channelrhodopsins from the unicellular green alga C. reinhardtii which are Light-gated cation channels, allowing fast light-induced depolarization of the plasma membrane (1,2). Mutations led to a slower photocycle and therefore to Channelrhodopsins with higher light sensitivity. Neuronal expression of Channelrhodopsin-2 (ChR2) yields Light-induced action potentials and Light-manipulated behaviour in C. elegans (3). The Light-activated chloride pump halorhodopsin (HR) from the archaeum Natronomonas pharaonis hyperpolarizes the plasma membrane and therefore allows Light-induced silencing of neurons (4). These two antagonistic rhodopsins may even be expressed in the same cell and still specifically be light-activated with 460 nm for ChR2 and 580 nm for HR. Recently we found a ChR2 mutant with increased expression and high light sensitivity (ChR2-XXL) which allows light modulation of deep brain neurons in adult Drosphila flies, even without feeding the chromophor all-trans retinal.

We heterologously expressed Photoactivated Adenylyl Cyclases (PAC) from Euglena gracilis (5,6) or bacteria (7,8), flavoproteins which quickly elevate cytoplasmic cyclic AMP by illumination with blue light in cultured cells and in living animals or plants. Now we engineered PAC proteins with an increased ratio of activity in the light vs. activity in the dark.

  1. References: 1: Nagel ... Hegemann (2002) Science 296: 2395-2398 2: Nagel ... Bamberg (2003) Proc Natl Acad Sci U.S.A. 100:13940-13945 3: Nagel ... Gottschalk (2005) Current Biology 15(24):2279-84. 4: Zhang ... Nagel, Gottschalk, Deisseroth (2007) Nature 446:633-639 5: Schröder-Lang ... Nagel (2007) Nat Methods 4(1):39-42 6: Looser ...Nagel G. (2009) Biol Chem. 390(11):1105-11 7: Stierl ... Nagel G, Hegemann P. (2011) J Biol Chem. 286(2):1181-8 8: Raffelberg ... Gärtner, Nagel (2013) Biochem J; 455(3):359-65