Actuation of delayed, high specificity negative feedback in the kaiabc cyanobacterial circadian oscillator

• Main Author: Phong, Connie
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2016
• Subjects: Biochemistry; Biophysics
• ISBN: 9781369129588; 1369129580

Circadian clocks are ubiquitous biological oscillators that coordinate behavior with the daily cycling of the environment. To ensure synchronization with the environment, the period of the endogenous clock must be maintained near 24 hours even as input signaling alters its amplitude and phase. I will describe work I’ve done to try to understand the molecular origins of robust periodicity using the biochemically tractable circadian oscillator from the cyanobacterium Synechococcus elongatus PCC 7942. In this simple three-protein oscillator timing information is encoded in the phosphorylation state of KaiC, a protein with two homologous catalytic domains in the RecA/DnaB superfamily of P-loop ATPases. I have defined separate functions for catalysis in each domain in generating phosphorylation rhythms. In particular I identified the C- terminal ATPase as being crucial to the generation of negative feedback needed to sustain oscillations. I will also describe how slow catalysis in the C-terminal ATPase acts as input- independent timer that permits the oscillator to respond to inputs signals while maintaining a robust circadian period. The inhibitory complexes that form between KaiB and KaiC to drive negative feedback are also highly specific to the serine-phosphorylated state of KaiC, and involve a novel structural change to KaiB. I will describe efforts to synthesize and integrate the various known biochemical features of KaiB!KaiC complex formation to show that they together constitute a regulatory circuit that ensures high specificity.