Biological clock8/24/2023 ![]() Looking ahead, the research team can see their findings having wider applications. Their work can serve as a research tool, helping scientists to better understand the mechanisms at work in the circadian clock cycle. “Our goal is to see all cyanobacterial clock proteins during the oscillation at an atomic level and to describe the moment that the ordered rhythm arises from chaotic atomic dynamics,” Furuike said. So thinking about their next steps, the team might use structural biology to reveal the atomic mechanisms of acceleration and deceleration of the gear rotations. The KaiC protein rhythmically activates and inactivates the reaction cycles autonomously to regulate assembly states of other clock-related proteins. ![]() We need to trace the structural changes of proteins patiently,” said Yoshihiko Furuike, assistant professor at the Institute for Molecular Science, National Institutes of Natural Sciences. “Because proteins are composed of a vast number of atoms, it is not easy to understand the mechanisms of their complicated but ordered functions. This coupling of the two gears drives the cyanobacterial circadian clock. Yet little was known about how allostery regulates the phosphorus cycle in KaiC.īy studying the KaiC in the eight distinct states, the team was able to observe a coupling that occurs in the phosphorus cycle and the ATPase hydrolysis cycle. In the past, scientists have studied the phosphorus cycle of the KaiC protein in vivio, in vitro, and in silico. The two cycles are mediated by hydrogen bonds among acidic, basic, and neutral components. The phosphorylation cycle and the ATP hydrolysis cycle occur in the double-ring structure of KaiC. Cooperative motion of two gears rotating in KaiC. To help them understand the basis for the allostery, they crystallized the KaiC protein in eight distinct states, allowing them to observe the cooperativity between the phosphorylation cycle and the ATP hydrolysis cycle working like two gears (Figure 2).įigure 2. The phosphorylation-ATP hydrolysis system works like a regulator for the cell activity. ![]() Phosphorylation cooperates with another reaction cycle, ATP hydrolysis, which is the energy consuming events determining the clock speed (Figure 2, upper panel). This detailed study of the atomic structures allowed them to cover the overall phosphorylation cycle, that process where a phosphate is transferred to the protein (Figure 2, lower panel). The team studied the atomic structures of the KaiC clock protein, by screening thousands of crystallization conditions. Allostery drives the cyanobacterial circadian clock. ![]() The team examined the structural basis for allostery, the complex changes that occur in shape and activity of the KaiC protein in the cyanobacteria (Figure 1, right lower panel). The blueish cyanobacteria are microorganisms that can be found in environments ranging from salt and fresh waters to soils to rocks. The cyanobacterial circadian clock is the simplest circadian clock as far as the number of its components, yet it is still a very complex system that can provide scientists with clues to the working of all circadian clocks. These biological clocks in organisms are composed of proteins (Figure 1, right upper panel). The team focused their research on KaiC, the clock protein that regulates the circadian rhythm in cyanobacteria, a type of bacteria lives in all types of water and are often found in blue-green algae (Figure 1, left panel). Circadian rhythms of the phosphorylation cycle (red circle with “P” indicating the phosphor transfer) and the ATP hydrolysis cycle (blue circle with “ATP” and “ADP” indicating the conversion of Adenosine-TriPhosphate into Adenosine-DiPhosphate) can be observed in a test tube. Clock proteins generating cyanobacterial circadian rhythms.
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