Dipping your hands into 160-degree water is guaranteed to give you an immediate and severe scalding—unless you're one of the few species of bacteria that manage to thrive in temperatures that would maim or kill the rest of the Earth's inhabitants. How these heat-loving bacteria manage to survive such intense temperatures has puzzled scientists for decades, but a researcher at the University of Rochester has uncovered a trick proteins may use to bolster bacteria against the searing heat.
"We've found a protein with a section that is flapping back and forth between two configurations like a flag in a storm," says Kara Bren, associate professor of chemistry at the University. "Nobody expected to find this. We've always expected high-temperature proteins to be rigid to bolster their structure in such an extreme environment, but we're seeing this unusual motion for the first time and it's opening up new ways of understanding how life manages to adapt to even the harshest environments."
The protein, which is found in a bacterium that lives in hot springs in Japan, had been a puzzle for scientists because its nuclear magnetic resonance spectrum—a sort of signature that reveals the structure of a molecule—was a confusing partial blur. Bren decided to investigate the meaning of the blur and found that it was actually a mixture of the two states of the flapping section, much like a quickly flapping flag might blur in a photograph.
The flapping process, called "fluxion," is the flapping of an amino acid about an iron ion within the protein. Fluxion has been observed in small synthetic molecules, but not within a protein. Previously this family of proteins was assumed to always have a highly rigid, defined structure at the crucial interior iron, so scientists were surprised to find one that had evolved such a complex behavior. Bren believes the scalding temperatures of the native cell's hot springs contributed to the protein's bizarre development.
"It may seem counter-intuitive, but having motion-enhancement in a protein like this could help stabilize it in extreme environments by increasing its inherent disorder," says Bren. Since proteins do their job by folding and unfolding their complicated structures, the more energy needed to unfold a protein, the more likely it is to stay folded and hence remain stable. If, in its folded state, the protein is able to shed energy by being "disorderly," then it has increased the amount of energy needed to unfold it. It's as if the flapping flag needs to be stilled by the 160-degree heat before the protein will break down.
Bren is working now to confirm the role fluxion plays in the stability of the protein, but she is also looking into the role the protein plays in the cell itself. Since the protein's structure is very similar to other proteins that perform crucial functions, Bren suggests that it may be involved in converting energy in the cell, such as in respiration or photosynthesis. The strange flapping may also contribute directly to the cell's function. Bren is working to determine if the switching section, a small organic group that regulates electron flow in these proteins, might be optimized to essentially fire electrons gathered through the protein's energy conversion processes in alternating directions. The behavior of partners working alongside Bren's protein may shed light on whether the flapping methyl group imparts another mysterious advantage that scientists haven't yet envisioned.
Beyond simply revealing that the environment of iron ions in living organisms are not necessarily the static structures researchers have always assumed, Bren's work may pave the way for future designer geneticists to enhance the stability of proteins needed in medicinal research. Even as NASA looks to Mars for signs of water and possible life, scientists now have a new way to understand how organisms can adapt to thrive in extreme environments such as those that may exist on other worlds in our solar system.
This research was funded by a grant from the National Institutes of Health.