The Control of Biological Rhythms by Phosphorylation

Posted by Melissa George on January 3rd, 2018

In order to investigate the key regulatory effects of phosphorylation modification on metabolic homeostasis and biorhythm, the researchers first studied the changes of protein phosphorylation in liver tissue of mice during two days using label-free quantification method. The results showed that in 25% of phosphorylated peptide segments, 40% of phosphorylated proteins, their phosphorylation levels were significantly fluctuating, and the ratio of serine, threonine and tyrosine was consistent with previous studies.

Time cluster analysis divided the proteins with periodic changes of phosphorylation level into two groups: high expression during day and high expression at night. Mice were inactive and active respectively. PCA analysis also classified phosphorylated proteins into two groups: high expression during day and high expression at night. At the same time, it was found that liver proteins with fluctuating phosphorylation levels were significantly enriched in specific metabolic pathways. For example, insulin related metabolic pathways, cell autophagy and circadian rhythms related metabolic pathways, suggested that post translational modification phosphorylation played a key role in regulating these metabolic processes in time dimension.

Later it was found that the expression levels of phosphorylation group and protein group were much different in different periods of a day. Difference in expression of phosphorylation was more serious, with 5 times with one day, which was significantly higher than the proteome level, while 80% of the phosphorylation cumulative intensity came from the 20% of the protein of phosphorylation level change, which showed that protein of phosphorylation level vibration was a regulatory protein rather than a structural protein.

The researchers found new the phosphorylation sites S446 and S440/441 on the CLOCK protein and its phosphorylation level also appeared cyclical change. Because the expression of CLOCK protein is constant, it indicated that the change of phosphorylation level was the main factor to control the rhythm of protein function. These results suggest that the central mechanism of rhythm regulation was the periodic change of protein phosphorylation level.

Further study on the specific and systematic effects of diurnal changes of protein phosphorylation level can not only deepen the interaction between biological rhythm and targeted metabolomics, but also further promote the progress of biological clock therapy.