The rising and setting of the sun causes dramatic oscillations in light and temperature. Organisms from bacteria to humans involuntarily anticipate these daily swings by means of an endogenous clock called the circadian clock. At the heart of the clock is an oscillator, which generates a ~24-h biochemical rhythm. This rhythm has a profound influence on metabolism, reproductive fitness, health, and disease. Yet, the molecular mechanism of circadian oscillators remains elusive. Due to the pervasive importance of circadian rhythms to virtually all life forms, this major gap in knowledge arguably has a broad impact on the field of life sciences.
The central focus of my laboratory is to fill in this major gap in knowledge by elucidating the timing mechanism of the circadian oscillator of cyanobacteria. Recently, we made some exciting findings that were highlighted by Chemical & Engineering News, PNAS, and Nature Reviews Microbiology.
The circadian oscillator of cyanobacteria.
The oscillator of the cyanobacterial clock is composed of only three proteins: KaiA, KaiB, and KaiC. When mixed together in a test tube with ATP, they generate a self-sustained circadian rhythm of phosphorylation of KaiC for several days. Our objective is to develop a comprehensive understanding of how a simple mixture of these three proteins keeps time.
Questions critical to our laboratory:
The mechanism of this oscillator remains far from understood. The most pressing questions for our laboratory include:
- How do KaiA and KaiB interact with KaiC, and how do these interactions regulate the autokinase and autophosphatase activities of KaiC?
- How does phosphorylation change KaiC such that its interactions with KaiA and KaiB change?
- Why are the kinetics of KaiC phosphorylation so slow?
- How does the clock protein SasA transduce the phosphorylation rhythm downstream along output pathways?
What our graduate students and postdocs are doing to answer these questions:
Students and postdocs apply the scientific method, and use an array of biochemical, chromatographic, and spectroscopic techniques, especially nuclear magnetic resonance spectroscopy, to test hypotheses formulated on our foundation of existing knowledge and new preliminary data. Recent discoveries by our lab led to exciting new insights on the molecular mechanism of this biological oscillator (see figure below):