Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Versatile Switch for Light-Controlled Cells

09.04.2015

Scientists from Jülich, Grenoble, Frankfurt and Moscow uncovered the atomic structure of KR2, a light-driven transporter for sodium ions which had only recently been discovered. Based on the structural information the team then identified a simple way to turn KR2 from a sodium- into a potassium pump using simple means.

Integrated into neurons, this could make KR2 a valuable tool for optogenetics, a new field of research that uses light-sensitive proteins as molecular switches to precisely control the activity of neurons and other electrically excitable cells using light impulses. The findings have been published in the journal Nature Structural and Molecular Biology.


The surface of the KR2 complex shown from the side. Each of the five KR2 molecules binds and transports a sodium ion (purple) across the membrane. The light-sensitive retinal inside the complex, which regulates pumping activity, is transparent.

Copyright: Forschungszentrum Jülich/IBS Grenoble


Left: Like all protein molecules, the KR2 pump consists of a single chain of amino acids folded into complex three-dimensional structure. Seven connected helices (yellow) form a channel inthe cell membrane through which sodium ions are transported. A structure unique among light-activated ion pumps is the additional short helix (blue) capping the outside opening of the pump like a lid. The pumping activity is driven by the small light-responsive retinal (green). Right: Under physiological conditions, five KR2 molecules spontaneously form a star-shaped pentameric complex.

Copyright: Forschungszentrum Jülich/IBS Grenoble

In 2013, scientists made an unexpected discovery while investigating the marine bacterium Krokinobacter eikastus. In its cellular membrane, the bacterium had a previously unknown type of ion transporter. The protein, which was dubbed KR2, belongs to a group of light-sensitive proteins that have become the basis of the research field of optogenetics.

When exposed to light, these proteins allow charged particles to flow into the cell or transport them outside the cell. Integrating these ion transporters into the neuronal membrane makes it possible to alter their state of charge using light impulses, thus enabling their activity to be precisely controlled. This method quickly became established in the neurosciences, in particular. However, only a few proteins are currently available for this and each of these proteins was only permeable to certain ions.

KR2 transports positively charged sodium ions out of the cell, which is a feature that so far had been missing in the toolkit of optogenetics. However, until now neither the exact atomic structure nor the ion transport mechanism had been known – which is an important prerequisite for utilizing KR2 and adapting it for specific applications.

This challenge awakened the interest of a team of structural biologists headed by Prof. Valentin Gordeliy, who heads research groups at the Institute of Complex Systems (ICS-6) at Forschungszentrum Jülich, Germany, at the Institute de Biologie Structurale in Grenoble, France, and at the Moscow Institute of Physics and Technology in Russia.

Using X-ray crystallography, the team obtained the first high-resolution 3D structural images of the single protein and the five-part complex that the KR2 molecule spontaneously forms under physiological conditions.

"The structure of KR2 has many unique features," says Ivan Gushchin, one of the lead authors of the study and a postdoc of Gordeliy. One of these features is a short protein helix capping the outfacing opening of the pump like a lid. A feature of KR2, that the scientists were particularly interested in was the unusual structure of the inward facing ion-uptake cavity, which was found to be unusually large and protruding from the protein surface. "We hypothesized that this structure could act as a kind of filter causing the selectivity of KR2 for sodium ions," Gushchin explains.

To put this idea to the test, Gordeliy´s team changed the structure by swapping specific amino acids at the site in question through targeted mutations. Not only did KR2 indeed lose its sodium-pumping ability; but also one of the mutations seemed to turn KR2 into a light-driven potassium pump – the first of its kind.

To accurately prove this observation the team performed a series of electrophysiological experiments with the purified protein in collaboration with Ernst Bamberg at the Max Planck Institute of Biophysics in Frankfurt am Main, who is an expert on membrane proteins and one of the founders of optogenetics.

For potential optogenetic application, this result is especially interesting, says Bamberg: "In neurons, transporting potassium ions from the cell is the natural mechanism of deactivation. Normally, an activated neuron will release them through passive potassium channels in the membrane. With a light-activated, active potassium pump this process could be precisely controlled."

This would make KR2 a very effective off-switch for neurons. Now, ways of integrating the pump into different types of cells need to be developed. "In combination with the light-activated Channelrhodopsin 2, which is used in labs worldwide as a molecular off-switch, the KR2 potassium pump would then form a perfect pair of tools for the precise control of nerve cell activity," says Bamberg.

Original publication:
Ivan Gushchin, Vitaly Shevchenko, Vitaly Polovinkin, Kirill Kovalev, Alexey Alekseev, Ekaterina Round, Valentin Borshchevskiy, Taras Balandin, Alexander Popov, Thomas Gensch, Christoph Fahlke, Christian Bamann, Dieter Willbold, Georg Büldt, Ernst Bamberg& Valentin Gordeliy:
Crystal structure of a light-driven sodium pump. Nature Structural & Molecular Biology (2015) doi:10.1038/nsmb.3002

Contact:

Prof. Dr. Valentin Gordeliy
Institute for Complex Systems, Structural Biochemistry (ICS-6)
Forschungszentrum Jülich
Institute de Biologie Structurale (CEA-CNRS-UJF), Grenoble
Tel: +49 2461 61-9509
E-Mail: g.valentin@fz-juelich.de, valentin.gordeliy@ibs.fr

Prof. Dr. Ernst Bamberg
Max Planck Institute of Biophysics, Frankfurt am Main
Tel:+49 69 6303-2000
E-Mail: secretary-bamberg@biophys.mpg.de

Press Contact:

Peter Zekert
Institute of Complex Systems, Strukturbiochemie (ICS-6)
Tel.: +49 (0) 2461 61-9711
E-Mail: p.zekert@fz-juelich.de

Weitere Informationen:

http://www.fz-juelich.de/SharedDocs/Pressemitteilungen/UK/EN/2015/15-04-09kr2-pu... Press release and images

Annette Stettien | Forschungszentrum Jülich

More articles from Life Sciences:

nachricht Single-stranded DNA and RNA origami go live
15.12.2017 | Wyss Institute for Biologically Inspired Engineering at Harvard

nachricht New antbird species discovered in Peru by LSU ornithologists
15.12.2017 | Louisiana State University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Error-free into the Quantum Computer Age

A study carried out by an international team of researchers and published in the journal Physical Review X shows that ion-trap technologies available today are suitable for building large-scale quantum computers. The scientists introduce trapped-ion quantum error correction protocols that detect and correct processing errors.

In order to reach their full potential, today’s quantum computer prototypes have to meet specific criteria: First, they have to be made bigger, which means...

Im Focus: Search for planets with Carmenes successful

German and Spanish researchers plan, build and use modern spectrograph

Since 2016, German and Spanish researchers, among them scientists from the University of Göttingen, have been hunting for exoplanets with the “Carmenes”...

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Single-photon detector can count to 4

18.12.2017 | Information Technology

Quantum memory with record-breaking capacity based on laser-cooled atoms

18.12.2017 | Physics and Astronomy

How much soil goes down the drain -- New data on soil lost due to water

18.12.2017 | Agricultural and Forestry Science

VideoLinks
B2B-VideoLinks
More VideoLinks >>>