Tanjef Szellas

Bio: Tanjef Szellas is an academic researcher from Max Planck Society. The author has contributed to research in topics: Bacteriorhodopsin & Chlamydomonas reinhardtii. The author has an hindex of 4, co-authored 4 publications receiving 2493 citations.

Channelrhodopsin-2, a directly light-gated cation-selective membrane channel.

Abstract: Microbial-type rhodopsins are found in archaea, prokaryotes, and eukaryotes. Some of them represent membrane ion transport proteins such as bacteriorhodopsin, a light-driven proton pump, or channelrhodopsin-1 (ChR1), a recently identified light-gated proton channel from the green alga Chlamydomonas reinhardtii. ChR1 and ChR2, a related microbial-type rhodopsin from C. reinhardtii, were shown to be involved in generation of photocurrents of this green alga. We demonstrate by functional expression, both in oocytes of Xenopus laevis and mammalian cells, that ChR2 is a directly light-switched cation-selective ion channel. This channel opens rapidly after absorption of a photon to generate a large permeability for monovalent and divalent cations. ChR2 desensitizes in continuous light to a smaller steady-state conductance. Recovery from desensitization is accelerated by extracellular H+ and negative membrane potential, whereas closing of the ChR2 ion channel is decelerated by intracellular H+. ChR2 is expressed mainly in C. reinhardtii under low-light conditions, suggesting involvement in photoreception in dark-adapted cells. The predicted seven-transmembrane α helices of ChR2 are characteristic for G protein-coupled receptors but reflect a different motif for a cation-selective ion channel. Finally, we demonstrate that ChR2 may be used to depolarize small or large cells, simply by illumination.

Channelrhodopsins: directly light-gated cation channels.

Abstract: Phototaxis and photophobic responses of green algae are mediated by rhodopsins with microbial type chromophores, i.e. all- trans -retinal in the ground state. The green alga Chlamydomonas reinhardtii was recently completely sequenced and the EST (expressed sequence tag) database was made public. We and others detected overlapping partial cDNA sequences that encode two proteins which we termed channelopsins (Chops). The N-terminal half of chop1 (∼300 of 712 amino acids) comprises hypothetical seven-transmembrane segments with sequence similarity to the proton pump bacteriorhodopsin and the chloride pump halorhodopsin. Even though the overall sequence homology is low, several amino acids are conserved that define the retinal-binding site and the H + -transporting network in BR (bacteriorhodopsin). Expression of Chop1, or only the hydrophobic core, in Xenopus laevis oocytes, enriched with retinal, produced a light-gated conductance (maximum at approx. 500 nm), which shows characteristics of a channel [ChR1 (channelrhodopsin-1)] that is selectively permeable for protons. Also ChR2 (737 amino acids) is an ion channel that is switched directly by light and also here the hydrophobic N-terminal half of the protein is sufficient to enable light-sensitive channel activity. The action spectrum is blue-shifted (maximum at approx. 460 nm) with respect to ChR1. In addition to protons, ChR2 is permeable to univalent and bivalent cations. We suggest that ChRs are involved in phototaxis of green algae. We show that heterologous expression of ChR2 is useful to manipulate intracellular p Ca or membrane potential of animal cells, simply by illumination.

Non-specific activation of the epithelial sodium channel by the CFTR chloride channel.

Abstract: The genetic disease cystic fibrosis is caused by mutation of the gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR). Controversial studies reported regulation of the epithelial sodium channel (ENaC) by CFTR. We found that uptake of 22Na+ through ENaC is modulated by activation of CFTR in oocytes, coexpressing CFTR and ENaC, depending on extracellular chloride concentration. Furthermore we found that the effect of CFTR activation could be mimicked by other chloride channels. Voltage– and patch–clamp measurements, however, showed neither stimulation nor inhibition of ENaC-mediated conductance by activated CFTR. We conclude that the observed modulation of 22Na+ uptake by activated CFTR is due to the effect of CFTR-mediated chloride conductance on the membrane potential. These findings argue against the notion of a specific influence of CFTR on ENaC and emphasize the chloride channel function of CFTR.

Millisecond-timescale, genetically targeted optical control of neural activity.

Abstract: Temporally precise, noninvasive control of activity in well-defined neuronal populations is a long-sought goal of systems neuroscience. We adapted for this purpose the naturally occurring algal protein Channelrhodopsin-2, a rapidly gated light-sensitive cation channel, by using lentiviral gene delivery in combination with high-speed optical switching to photostimulate mammalian neurons. We demonstrate reliable, millisecond-timescale control of neuronal spiking, as well as control of excitatory and inhibitory synaptic transmission. This technology allows the use of light to alter neural processing at the level of single spikes and synaptic events, yielding a widely applicable tool for neuroscientists and biomedical engineers.

The Development and Application of Optogenetics

Abstract: Genetically encoded, single-component optogenetic tools have made a significant impact on neuroscience, enabling specific modulation of selected cells within complex neural tissues. As the optogenetic toolbox contents grow and diversify, the opportunities for neuroscience continue to grow. In this review, we outline the development of currently available single-component optogenetic tools and summarize the application of various optogenetic tools in diverse model organisms.

Multimodal fast optical interrogation of neural circuitry

Abstract: Our understanding of the cellular implementation of systems-level neural processes like action, thought and emotion has been limited by the availability of tools to interrogate specific classes of neural cells within intact, living brain tissue. Here we identify and develop an archaeal light-driven chloride pump (NpHR) from Natronomonas pharaonis for temporally precise optical inhibition of neural activity. NpHR allows either knockout of single action potentials, or sustained blockade of spiking. NpHR is compatible with ChR2, the previous optical excitation technology we have described, in that the two opposing probes operate at similar light powers but with well-separated action spectra. NpHR, like ChR2, functions in mammals without exogenous cofactors, and the two probes can be integrated with calcium imaging in mammalian brain tissue for bidirectional optical modulation and readout of neural activity. Likewise, NpHR and ChR2 can be targeted together to Caenorhabditis elegans muscle and cholinergic motor neurons to control locomotion bidirectionally. NpHR and ChR2 form a complete system for multimodal, high-speed, genetically targeted, all-optical interrogation of living neural circuits.

Multimodal fast optical interrogation of neural circuitry

Abstract: Our understanding of the cellular implementation of systems-level neural processes like action, thought and emotion has been limited by the availability of tools to interrogate specific classes of neural cells within intact, living brain tissue. Here we identify and develop an archaeal light-driven chloride pump (NpHR) from Natronomonas pharaonis for temporally precise optical inhibition of neural activity. NpHR allows either knockout of single action potentials, or sustained blockade of spiking. NpHR is compatible with ChR2, the previous optical excitation technology we have described, in that the two opposing probes operate at similar light powers but with well-separated action spectra. NpHR, like ChR2, functions in mammals without exogenous cofactors, and the two probes can be integrated with calcium imaging in mammalian brain tissue for bidirectional optical modulation and readout of neural activity. Likewise, NpHR and ChR2 can be targeted together to Caenorhabditis elegans muscle and cholinergic motor neurons to control locomotion bidirectionally. NpHR and ChR2 form a complete system for multimodal, high-speed, genetically targeted, all-optical interrogation of living neural circuits.