Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Synthetic proteins help solve structure of the fluoride ion channel

08.09.2015

Unexpected double-barreled 'channsporter' structure suggests new mechanism for ion transport

Although present almost everywhere - food, soil, toothpaste and especially tap water -, the fluoride ion is highly toxic to microorganisms and cells. To avoid death, cells must remove fluoride that has accumulated inside them, a process accomplished via ion channels - protein tunnels through the cell membrane that only allow specific substances to pass through.


This is a representation of the fluoride ion channel (center) with monobodies attached (top and bottom). Monobodies expanded the surface area of the ion channel and aligned it so that its structure could be solved.

Credit: Stockbridge et al., Nature

Fluoride ion channels have only recently been discovered, and studies have hinted at an unusual structure that might explain their remarkable selectivity for fluoride. However, these channels are small and have been extremely challenging to crystallize, which has thus far prevented investigations of their atomic structure.

In a study published in Nature on Sept. 7, 2015, an international team of scientists overcame these limitations and for the first time resolved the atomic structure of a fluoride ion channel. They discovered a unique "double-barreled" architecture that contains two pathways through which fluoride ions flow, representing a new mechanism of ion transport. Their findings shed light on the evolution of these channels and enable new approaches to modify their function, with potential applications such as the development of novel antibiotics.

The key technological innovation that enabled this achievement was the use of monobodies - small, synthetic proteins that can be custom-designed to bind to highly specific locations on target proteins. Monobodies were engineered to function as 'crystallization chaperones' that stabilized and aligned fluoride ion channels so their structure could be determined.

"It is very clear that synthetic binding technologies are now mature," said study co-author Shohei Koide, PhD, professor of biochemistry and molecular biophysics at the University of Chicago and a world-leader in monobody research and design. "Monobodies are refined and powerful enough to attack important questions in biology and medicine, such as the structure of the fluoride ion channel, but they can also be used to generate molecules that are almost immediately useful in industry. It's exciting to us as we continue to reveal the many possibilities of this powerful technology."

The Fluc family of fluoride ion channels were recently discovered, and studies by a team led by Christopher Miller, PhD, HHMI Investigator and professor of biochemistry at Brandeis University, found that they are among the most selective channels yet identified. It has remarkable specificity for fluoride and can distinguish it from the closely related chloride ion.

To determine the atomic structure of these channels, a technique known as x-ray crystallography must be used. This requires that the channel protein be purified and crystallized (aligned in a highly ordered, reproducible manner). However, membrane proteins are unstable when removed from their native environment. To circumvent this, traditional biochemical techniques use detergent compounds to mask and stabilize the surface areas that once resided in cell membrane, allowing crystallization to occur.

For the fluoride ion channel, the surface area that is covered by detergent compounds proved to be too much for crystal formation to occur, due to the channel's small size and almost complete embedment within the membrane.

To address this challenge, Koide, Miller and their teams designed monobodies that bound to target locations on the fluoride ion channel - specifically, two small surfaces not embedded within the cell membrane. This dramatically expanded the surface area that could be used to crystallize the channels. In addition, monobodies have certain properties that allow them to align with each other in a highly-reproducible fashion, further enabling the creation of a stable lattice. The two groups further collaborated with Simon Newstead, PhD, and his team from the University of Oxford, and utilized new crystallization technology for membrane proteins. This three-way collaboration yielded the atomic structure of the channel.

The researchers discovered that the fluoride ion channel is comprised of two major building blocks, which assemble together in an antiparallel manner. Most typical ion channels have only one pore through which ions¬¬ flow in the entire channel assembly, but the Fluc channel was found to have two. This architecture resembles another class of membrane proteins called transporters that use energy to actively pump ions across the cell membrane. However, Fluc channels do not require energy. This similarity and distinction led the researchers to propose that the term "channsporter" could be applied to these channels.

"The function of this molecule is a channel, but the architecture is more like a transporter," Koide said. "Evolutionarily, it's quite interesting. It requires further study, but this protein appears as if it evolved from something that probably had antiparallel geometry that was important for integrity, not necessarily function."

The monobodies also represent the first known molecules, natural or synthetic, that block a Fluc channel. The structure with a blocker allowed a deeper analysis of how fluoride ions flow through the channel. While this study has provided clues as to the channel's remarkable sensitivity, additional studies are underway to further elucidate its physical dynamics.

The ability to specifically block the ion channel with monobodies also raises intriguing possibilities for translational applications. For example, blocking the fluoride ion channel in undesirable microorganisms such as pathogenic bacteria would cause a lethal accumulation of fluoride when they are exposed to something as common as tap water. This could represent a completely new strategy for the development of potent antibiotics.

"With the structure now known, we can figure out exactly how fluoride ion channels work and how to control their function," Koide said. "It's blue sky, but we can certainly envision making different inhibitors of channels with monobodies, which could perhaps be targeted against harmful cells and microorganisms."

"For now, this study represents a proof of concept that monobodies can be designed to work with very difficult targets to make inhibitors and determine structural information," he adds. "We are now working with collaborators on similar applications in many other systems."

###

The study, "Crystal structures of a double-barreled fluoride ion channel," was supported by the Wellcome Trust and the National Institutes of Health. Additional authors include Akiko Koide from the University of Chicago, and Randy B. Stockbridge, Ludmila Kolmakova-Partensky and Tania Shane from HHMI at Brandeis University.

Kevin Jiang | EurekAlert!

More articles from Life Sciences:

nachricht Stingless bees have their nests protected by soldiers
24.02.2017 | Johannes Gutenberg-Universität Mainz

nachricht Antimicrobial substances identified in Komodo dragon blood
23.02.2017 | American Chemical Society

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

NASA eyes Pineapple Express soaking California

24.02.2017 | Earth Sciences

New gene for atrazine resistance identified in waterhemp

24.02.2017 | Agricultural and Forestry Science

New Mechanisms of Gene Inactivation may prevent Aging and Cancer

24.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>