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Scientists at Texas A&M University have found evidence that a protein which regulates the internal circadian clock of the cyanobacterium Synechococcus elongatus, a freshwater blue-green algae, is in fact controlled by a cofactor that can affect its circadian rhythm -- a finding which may shed more light on how organisms from bacteria to mammals receive and interpret environmental cues.

Researchers Dr. David P. Barondeau, assistant professor of chemistry at Texas A&M, along with chemistry graduate student Jennifer Bridwell-Rabb of the Texas A&M Chemistry/Biology Interface (CBI) Training Program and biochemistry-biophysics postdoctoral research associate Thammajun L. Wood of the Texas A&M Center for Biological Clocks Research (CBCR) are collaborating with former Texas A&M professor Dr. Susan S. Golden and her team at the Center for Chronobiology and Division of Biological Sciences at the University of California-San Diego and Dr. Andy LiWang and his team at the University of California-Merced in the ongoing project to study KaiA, KaiB and KaiC, the proteins that control the circadian clock rhythm of S. elongatus and other bacteria.

Long thought to be a biological feature of only eukaryotes, or complex-celled organisms, circadian clocks are the 24-hour cycle that determines an organism's biological clock. Researchers only recently discovered that unicellular cyanobacteria possess a circadian clock as well, noting that they would go through photosynthesis during the day and then switch to the incompatible process of nitrogen fixation at night when oxygen levels are low. They determined that the organism used the circadian clock to separate the two processes.

In their current analysis of S. elongatus, the Texas A&M-led team found that the quinone analog 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) binds to KaiA, the modulator of its circadian clock, which directly senses environmental signals as changes in its oxidation-reduction (redox) state, thereby affecting its circadian clock. This, in turn, implies a correlation between redox and circadian rhythm.

The team's results are published in the Proceedings of the National Academy of Sciences (PNAS) Online Early Edition for the week of March 15-19.

"This is the biggest clue we have found so far," said Bridwell-Rabb. "We didn't know how environmental information is relayed to the oscillator to create these rhythms, so by KaiA binding this cofactor, it's a direct link to environmental cues in redox and changing the rhythm."

Cyanobateria has a very simple circadian clock in comparison to other multi-celled organisms. However, understanding its functions could have significant implications that could one day lead to a better understanding of the more complicated circadian clock in humans and other mammals.

Things that blunt our normal routines, such as sleep disorders or jet lag, could be better understood or even fixed, Barondeau noted.

"Humans have multiple circadian oscillators, and they are much more complex," Barondeau said. "Cyanobacteria have a very simple biological clock. When it was discovered that these single-celled organisms have one, it became a really exciting opportunity for an in-depth study. The circadian clock is implicated in human health, including cancer and depression."

In the meantime, Barondeau and Bridwell-Rabb hope to expand their work with the proteins in cyanobacteria and their relation to its circadian rhythm.

"It's interesting how environmental signals are used to modify the clock," Barondeau said. "We want to continue with more detailed structural investigations."

-aTm-

Contact: Chris Jarvis, (979) 845-7246 or cjarvis@science.tamu.edu or Dr. David P. Barondeau, (979) 458-0735 or barondeau@chem.tamu.edu

Jarvis Chris

  • Dr. David P. Barondeau

  • Structure of KaiA

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