Regulation mechanisms of the dual ATPase in KaiC

Computation Implemented by the Interaction of Chemical Reaction, Clustering, and De-Clustering of Molecules

A chemical reaction and its reaction environment are intrinsically linked, especially within the confines of narrow cellular spaces. Traditional models of chemical reactions often use differential equations with concentration as the primary variable, neglecting the density heterogeneity in the solution and the interaction between the reaction and its environment. We model the interaction between a chemical reaction and its environment within a geometrically confined space, such as inside a cell, by representing the environment through the size of molecular clusters. In the absence of fluctuations, the interplay between cluster size changes and the activation and inactivation of molecules induces oscillations. However, in unstable environments, the system reaches a fluctuating steady state. When an enzyme is introduced to this steady state, oscillations akin to action potential spike trains emerge. We examine the behavior of these spike trains and demonstrate that they can be used to implement logic gates. We discuss the oscillations and computations that arise from the interaction between a chemical reaction and its environment, exploring their potential for contributing to chemical intelligence.

The inner workings of an ancient biological clock

Circadian clocks evolved in diverse organisms as an adaptation to the daily swings in ambient light and temperature that derive from Earth's rotation. These timing systems, based on intracellular molecular oscillations, synchronize organisms' behavior and physiology with the 24-h environmental rhythm. The cyanobacterial clock serves as a special model for understanding circadian rhythms because it can be fully reconstituted in vitro. This review summarizes recent advances that leverage new biochemical, biophysical, and mathematical approaches to shed light on the molecular mechanisms of cyanobacterial Kai proteins that support the clock, and their homologues in other bacteria. Many questions remain in circadian biology, and the tools developed for the Kai system will bring us closer to the answers.

Structure-function relationship of KaiC around dawn

KaiC is a multifunctional enzyme functioning as the core of the circadian clock system in cyanobacteria: its N-terminal domain has adenosine triphosphatase (ATPase) activity, and its C-terminal domain has autokinase and autophosphatase activities targeting own S431 and T432. The coordination of these multiple biochemical activities is the molecular basis for robust circadian rhythmicity. Therefore, much effort has been devoted to elucidating the cooperative relationship between the two domains. However, structural and functional relationships between the two domains remain unclear especially with respect to the dawn phase, at which KaiC relieves its nocturnal history through autodephosphorylation. In this study, we attempted to design a double mutation of S431 and T432 that can capture KaiC as a fully dephosphorylated form with minimal impacts on its structure and function, and investigated the cooperative relationship between the two domains in the night to morning phases from many perspectives. The results revealed that both domains cooperate at the dawn phase through salt bridges formed between the domains, thereby non-locally co-activating two events, ATPase de-inhibition and S431 dephosphorylation. Our further analysis using existing crystal structures of KaiC suggests that the states of both domains are not always in one-to-one correspondence at every phase of the circadian cycle, and their coupling is affected by the interactions with KaiA or adjacent subunits within a KaiC hexamer.