Biological clock tick-tocks at protein level

Scientists show how single protein runs circadian clock in photosynthesizing bacteria

Photo by: Wikipedia
Photo by: Wikipedia

Updated Jul 28, 2015

Researchers from the University of California (UC) demonstrated how the KaiB protein runs the circadian clock in cyanobacteria –photosynthesizing organisms which need sunlight to sustain life functions.

“The circadian clock drives powerful rhythms of rest and activity," lead researcher Andy LiWang said in the UC Merced press release.

“Normally, your internal clock is synchronized with local time. At night, you feel tired, and in the morning, you feel ready to take on the world.”

LiWang and his teams choose cyanobacteria for its simplicity since three proteins driving its timekeeping mechanism –KaiA, KaiB, and KaiC– can be reassembled in a test tube without the complexity of living cells.

According to the findings of the study, switching between two distinct three-dimensional folds of the KaiB protein initiates the shift of the circadian cycle by binding KaiC and capturing KaiA which signals the organism to prepare for sunrise every day.

“If you mix cyanobacterial clock proteins in a test tube with an energy source, the test tube literally starts ticking,” LiWang said. “You can tell time by it. How do these clocks manage to go at a 24-hour pace?”

In another separate study, Japanese researchers showed how Earth’s daily rotation duration is encoded in the 10 nm KaiC protein in cyanobacterial cells.

The study finds that KaiC ATPase activity, ATP hydrolysis reaction mediator, shows a circadian oscillation even in the absence of KaiA and KaiB. This signal had a frequency of 0.91-1 which coincides with the 24-hour period.

“The authors of this study discovered that the Earth's daily rotation period (24 hours) is implemented as the time constant of the feedback mechanism mediated in this protein structure,” the press release of the Japanese study wrote.

Both studies are published online on June 25 in Science Express and soon will be published in print in the journal of Science.