Dept. of Biophysical Chemistry

Max-von-Laue-Str. 3, 60438, Frankfurt/Main, Germany

The cystic fibrosis
chloride channel and
Channelrhodopsins

Dr. phil. nat. University of Frankfurt, 1988
Postdoc, Yale University, 1988 - 1989
Postdoc, The Rockefeller University, 1990 - 1992
Habilitation (in Biophysical Chemistry), University of Frankfurt, 1998
At the Institute since 1992

E-mail: Dr. Georg Nagel

PREVIOUS AND CURRENT RESEARCH

CFTR: The plasma membrane anion channel CFTR is defective in the hereditary disease Cystic Fibrosis (“Mukoviszidose”). We express human CFTR in oocytes from Xenopus laevis . For investigation of the kinetics of ATP-induced gating of CFTR channels, we are using fast solution changes of nucleotides or laser-induced photolysis of caged ATP. CFTR is often portrayed as serving several functions: apart from its function as anion channel, a regulatory function was proposed by several groups. Especially there seems to be a regulatory interaction of CFTR with the epithelial Na⁺ channel (ENaC). In an attempt to reveal molecular mechanisms of this interaction, we were surprised to find that the effect of CFTR activation on ENaC is not based on specific interaction. We then revealed the biophysical basis of apparent interaction of CFTR and ENaC: a previously reported activation of ENaC by CFTR in the sweat gland is due to electrochemical coupling and may only be observed in membrane potential measurements, i.e. if the membrane is not voltage-clamped. However, the previously reported specific inhibition of ENaC by activation of CFTR in voltage-clamped oocytes is based on an artifact, due to a series resistance in the measuring circuit, which leads to seriously faulted voltage-clamp results (Nagel et al., 2001); see also:

http://central.igc.gulbenkian.pt/cftr/newsletters/newsletters_files/newsletter_september_2001.pdf

and:

http://central.igc.gulbenkian.pt/cftr/vr/d/nagel_cftr_investigated_with_the_two_electrode_voltage_clamp_technique.pdf

Channelrhodopsins: Green algae were postulated to contain microbial type rhodopsins, seven transmembrane proteins with a covalently linked all-trans retinal as chromophor, like the archaebacterial light-driven proton pump Bacteriorhodopsin. These photoreceptors trigger a signalling chain which enables them to find optimal light conditions. From Peter Hegemann, Univ. Regensburg, we obtained cDNA from the unicellular green alga Chlamydomonas reinhardtii, predicted to code for microbial type retinal proteins. After expression in oocytes, electrophysiological analysis identified one of them as a light-sensitive proton channel, the first directly light-gated Ion Channel, which we named Channelrhodopsin-1, see Fig. 2 (Nagel et al., 2002). Currently we are analyzing Channelrhodopsin-2, a directly light-gated Cation Channel. With the Channelrhodopsins we discovered a new family of Ion Channels: simple proteins which are directly opened by light. First site-directed mutagenesis experiments revealed functional important amino acid residues. Recently we succeeded in functional expression of Channelrhodopsins in mammalian cells. We suggest that Channelrhodopsins may be useful to depolarize cells, simply by illumination.

FUTURE PROJECTS

We will continue to study reported interactions of CFTR with membrane transporters as well as molecular mechanisms of CFTR activation and salt secretion. The molecular mechanism of ion transfer in Channelrhodopsins is our next challenge. We are also interested in biotechnological applications of channelrhodopsins and other light-activated plant proteins. 

GROUP MEMBERS

Ph.D. students:
	Nona Adeishvili		Nona Adeishvili
	Bettina Himmel		Bettina Himmel
	Taryn Kirsch		Taryn Kirsch
	Saskia Schröder-Lang		Saskia Schröder-Lang
Technical assistant:
	Doris Ollig		Doris Ollig

SELECTED PUBLICATIONS

Weinreich F, Riordan JR, Nagel G.: Dual effects of ADP and AMP-PNP on CFTR kinetics show binding to two different nucleotide binding sites. J. Gen. Physiol. 114:55-70 (1999)

Nagel, G.: Differential function of the two nucleotide binding domains on CFTR. BBA Biomembranes, 1461, 263-274 (Review), (1999)

Budiman T, Bamberg E, Koepsell H, Nagel G.: Mechanism of electrogenic cation transport by the cloned organic cation transporter 2 from rat. J Biol Chem. 275: 29413-20. (2000)

Nagel, G., Szellas, T., Riordan, J.R., Friedrich, T., Hartung, K.: Non-specific activation of the epithelial sodium channel by the CFTR chloride channel. EMBO Reports 2: 249-254 (2001)

Schmies G, Engelhard M, Wood PG, Nagel G, Bamberg E.: Electrophysiological characterization of specific interactions between bacterial sensory rhodopsins and their transducers. Proc Natl Acad Sci U S A. 98:1555-1559. (2001)

Powe A, Zhou Z, Hwang T-C, Nagel G.: Quantitative Analysis of ATP-Dependent Gating of CFTR. Methods in Molecular Medicine, vol 70: Cystic Fibrosis Methods and Protocols: pages 67-98. Edited by W.R. Skach. Humana Press Inc., Totowa, NJ, USA. (2002)

Nagel G., D. Ollig, M. Fuhrmann, S. Kateriya, A.M. Musti, E. Bamberg, P. Hegemann: Channelrhodopsin-1: a light-gated proton channel in green algae. Science 296: 2395-2398 (2002)

DIPLOMA THESES

Tanjef Szellas: Elektrophysiologische Charakterisierung des Natrium-Iodid-Symporters, Frankfurt/Main 1999.

Saskia Schröder-Lang: Untersuchungen zur postulierten Interaktion zwischen CFTR und dem endogenen Ca²⁺-aktivierten Cl^--Kanal in Oozyten von Xenopus laevis, Darmstadt 2002.

Ph.D. THESES

Thomas Budiman: Elektrophysiologische Charakterisierung des Transporters für organische Kationen rOCT2, Frankfurt/Main 2001

Tanjef Szellas: Die Regulation des CFTR, Frankfurt/Main 2002.

GRANT SUPPORT

Deutsche Forschungsgemeinschaft (DFG)

INVITED LECTURES

Int. Ph.D. Summer School “Membrane Chemistry ”, Copenhagen, DK, 2000
Göttinger Transporttag, Univ. Göttingen, 2000
Universität Konstanz, 2001
FEBS course on ABC proteins, Gosau, Austria, 2001
EU-CFTR-meeting in Estoril, Portugal, 2001
Transportkolloquium in Rauischholzhausen, 2001
Forschungszentrum Jülich, 2002
Int. Conf. on Lab. Med. & Eur. Conf. of Clin. Mol. Biology, Capri, Italy, 2002
EU-CFTR-meeting in Sintra, Portugal, 2002
Annual meeting of Dt. Gesellschaft für Biophysik, Dresden, 2002
Telethon, Milan, Italy, 2002
Conference on Bionergetics of Microorganisms, Oberreifenberg/Taunus, 2003
Universität Würzburg, 2003