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Interaction of circadian clock proteins PER2 and CRY with BMAL1 and CLOCK
Sonja Langmesser1, Tiziano Tallone, Alain Bordon
1Department of Medicine, Division of Biochemistry, University of Fribourg, Rue du Musée 5, 1700 Fribourg, Switzerland. sonja.langmesser@unifr.ch
Background:
Circadian oscillation of clock-controlled gene expression is mainly regulated at the transcriptional level. Heterodimers of CLOCK and BMAL1 act as activators of target gene transcription; however, interactions of PER and CRY proteins with the heterodimer abolish its transcriptional activation capacity. PER and CRY are therefore referred to as negative regulators of the circadian clock. To further elucidate the mechanism how positive and negative components of the clock interplay, we characterized the interactions of PER2, CRY1 and CRY2 with BMAL1 and CLOCK using a mammalian two-hybrid system and co-immunoprecipitation assays.
Results:
Both PER2 and the CRY proteins were found to interact with BMAL1 whereas only PER2 interacts with CLOCK. CRY proteins seem to have a higher affinity to BMAL1 than PER2. Moreover, we provide evidence that PER2, CRY1 and CRY2 bind to different domains in the BMAL1 protein.
Conclusion:
The regulators of clock-controlled transcription PER2, CRY1 and CRY2 differ in their capacity to interact with each single component of the BMAL1-CLOCK heterodimer and, in the case of BMAL1, also in their interaction sites. Our data supports the hypothesis that CRY proteins, especially CRY1, are stronger repressors than PER proteins.
Insights
The circadian clock
Area of Science:
- Molecular Biology
- Chronobiology
- Genetics
Background:
- Circadian rhythms rely on clock-controlled gene expression, primarily regulated transcriptionally.
- CLOCK-BMAL1 heterodimers activate transcription, while PER and CRY proteins repress it.
- Understanding the interplay between positive and negative clock regulators is crucial.
Purpose of the Study:
- To investigate the interaction mechanisms between PER2, CRY1, CRY2, and the CLOCK-BMAL1 heterodimer.
- To clarify how negative regulators (PER, CRY) interact with positive regulators (CLOCK, BMAL1) in the circadian clock.
Main Methods:
- Mammalian two-hybrid system assays were employed.
- Co-immunoprecipitation assays were utilized to study protein interactions.
Main Results:
- PER2 and CRY proteins interact with BMAL1; PER2 also interacts with CLOCK.
- CRY proteins exhibit a higher affinity for BMAL1 than PER2.
- PER2, CRY1, and CRY2 bind to distinct domains on the BMAL1 protein.
Conclusions:
- PER2, CRY1, and CRY2 display differential binding capacities and sites with BMAL1 and CLOCK components.
- CRY proteins, particularly CRY1, function as more potent repressors of the circadian clock than PER proteins.
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