Reversible phosphorylation subserves robust circadian rhythms by creating a switch in inactivating the positive...

Area of Science:

• Chronobiology
• Molecular Biology
• Systems Biology

Background:

• Circadian rhythms rely on protein phosphorylation, a process crucial for generating biological timing.
• Negative feedback loops are common mechanisms driving circadian rhythms.
• The Neurospora crassa circadian clock involves the FREQUENCY (FRQ) protein and the White Collar Complex (WCC).

Purpose of the Study:

• To develop a minimal model of the Neurospora crassa circadian clock.
• To investigate the role of FRQ-dependent WCC phosphorylation in circadian rhythm generation.
• To understand how posttranslational modifications contribute to robust circadian timing.

Main Methods:

• Computational modeling of the core negative feedback loop in the Neurospora crassa circadian clock.
• Analysis of FRQ-WCC interactions and their impact on WCC activity.
• Simulations to assess model's ability to reproduce known clock behaviors.

Main Results:

• The model successfully replicated key circadian features like period length and entrainment.
• FRQ controls WCC activity in a switch-like manner via zero-order ultrasensitivity.
• Active WCC exhibits robust, spiky oscillations, sufficient for driving circadian output.
• Low cooperativity in transcriptional activation is adequate for robust circadian rhythms.

Conclusions:

• The core negative feedback loop and FRQ phosphorylation ensure robust circadian rhythms in Neurospora.
• Posttranslational modifications, specifically phosphorylation, play critical roles in circadian clock function.
• Switch-like control of the positive element (WCC) by the negative element (FRQ) is key to rhythm robustness.