NJIT Physics Dept - MtSE Joint Seminar

December 4th, Monday

Magnesium Regulates the Circadian Oscillator in Cyanobacteria

Prof. Yong-Ick Kim

Dept. of Chemistry and Environmental Science, NJIT (Biophysics/Materials Science, Host: Dias)

Time: 11:45am-12:45pm with 11:30am tea time

Room: FMH 408 (**SPECIAL ROOM**)

The circadian clock controls 24-hour biological rhythms in our body, influencing many time-related activities such as sleep and wake. The simplest circadian clock is found in cyanobacteria, with the proteins KaiA, KaiB, and KaiC generating a self-sustained circadian oscillation of KaiC phosphorylation and dephosphorylation. KaiA activates KaiC phosphorylation by binding the A-loop in KaiC, while KaiB attenuates it by sequestering KaiA from the A-loop. Structural analysis revealed that magnesium regulates the phosphorylation and dephosphorylation of KaiC by association or dissociation with catalytic Glu residues that activate phosphorylation. In the absence of KaiA, high magnesium concentration made KaiC dephosphorylate, whereas low magnesium concentration made KaiC phosphorylate. KaiC alone behaved as an hourglass-type timekeeper when magnesium concentration was alternated between low and high levels in vitro. The magnesium concentration in cyanobacteria in vivo was lower in light than in darkness. Our findings suggest how a circadian oscillator evolved from an hourglass timer to a self-sustained oscillator at a mechanistic level.