Wild and weird world of fluoride channels: Researchers discover how microbes survive the ubiquitous toxic ion

Sep 19, 2013 by Leah Burrows
E. coli bacteria are protected from toxic fluoride by channel proteins. Credit: istockphoto

It's not just in toothpaste and mouthwash—fluoride is found in just about everything from rocks and water to the soil and the sea. It is the 13th most abundant element in the Earth's crust, and it's extremely toxic to single-celled organisms such as bacteria and yeasts. 

Yet these organisms survive and even flourish in fluoride-rich environments. How?

Brandeis University scientists have an answer that may have implications for the treatment of bacterial diseases such as tuberculosis. 

In a paper published in August in the journal eLife, professor of biochemistry Christopher Miller reports have evolved an unusual fluoride-specific ion channel to export toxic fluoride from the cell. Postdoctoral researchers Randy Stockbridge, Janice Robertson and Ludmila Kolmakova-Partensky contributed to the paper. 

Ions are electrically charged molecules that need help from one of two types of membrane transport proteins—carriers and channels—to cross cell membranes. Carriers act like taxis, ferrying ions into and out of the cell. Channel proteins are more like one-way tunnels, forming a pore in the that transports ions from areas of high concentration to areas of low concentration.

Fluoride ions are sneaky. They seep into cells in protonated form—as hydrofluoric acid—and when the acid breaks down in the cell's higher pH, only the fluoride remain. Since hydrofluoric acid is easily able to permeate cell membranes, cells accumulate fluoride at higher levels than their extracellular environments. 

Wild and weird world of fluoride channels: Researchers discover how microbes survive the ubiquitous toxic ion
Fluoride (F-), highlighted in green, in the binding site of an exporter.

That accumulation activates a family of transport proteins, called Fluc, to build a channel so specific that it can distinguish between the harmful fluoride and the closely related but harmless chloride, making it the most selective channel yet discovered. The channel is also unusual in that its structure is upside down and backwards from every other studied. 

"This newly discovered violates all the rules of known channels," says Miller, who is also an investigator with the Howard Hughes Medical Institute. 

In examining how this channel works, Miller and his team disabled a microbe's internal security system by using a bacterial strain whose Fluc gene is knocked out. When these bugs are exposed to fluoride, the ion accumulates and inhibits the production of energy by glycolysis and the synthesis of DNA and RNA. Miller and his team could then replace the Fluc gene, or similar genes from other organisms, to rescue the bacteria from this hypersensitivity to fluoride. 

Since fluoride is mostly non-toxic to humans (but don't eat your toothpaste), this strategy may be one avenue to explore in developing treatments for harmful , Miller says. But for the moment, the channel's weird, wild structure is captivating enough.

Explore further: New evidence on how fluoride fights tooth decay

Related Stories

New evidence on how fluoride fights tooth decay

May 01, 2013

In an advance toward solving a 50-year-old mystery, scientists are reporting new evidence on how the fluoride in drinking water, toothpastes, mouth rinses and other oral-care products prevents tooth decay. ...

Herbal defluoridation of drinking water

Mar 05, 2013

Researchers in India have developed a filter system based on a medicinal herb, which they say can quickly and easily remove "fluoride" from drinking water. The technology described in the March issue of the International Jo ...

Recommended for you

Researchers successfully clone adult human stem cells

Apr 18, 2014

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Researchers develop new model of cellular movement

Apr 18, 2014

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

User comments : 0

More news stories

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.

Low tolerance for pain? The reason may be in your genes

Researchers may have identified key genes linked to why some people have a higher tolerance for pain than others, according to a study released today that will be presented at the American Academy of Neurology's 66th Annual ...

How to keep your fitness goals on track

(HealthDay)—The New Year's resolutions many made to get fit have stalled by now. And one expert thinks that's because many people set their goals too high.