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Updated: Feb 12, 2026

Monitoring Cell-autonomous Circadian Clock Rhythms of Gene Expression Using Luciferase Bioluminescence Reporters
Published on: September 27, 2012
Circadian clock activity of cryptochrome relies on tryptophan-mediated photoreduction
Changfan Lin1, Deniz Top2, Craig C Manahan1
1Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853.
Abstract:
Cryptochromes (CRYs) entrain the circadian clocks of plants and animals to light. Irradiation of the Drosophila cryptochrome (dCRY) causes reduction of an oxidized flavin cofactor by a chain of conserved tryptophan (Trp) residues. However, it is unclear how redox chemistry within the Trp chain couples to dCRY-mediated signaling. Here, we show that substitutions of four key Trp residues to redox-active tyrosine and redox-inactive phenylalanine tune the light sensitivity of dCRY photoreduction, conformational activation, cellular stability, and targeted degradation of the clock protein timeless (TIM). An essential surface Trp gates electron flow into the flavin cofactor, but can be relocated for enhanced photoactivation. Differential effects of Trp-mediated flavin photoreduction on cellular turnover of TIM and dCRY indicate that these activities are separated in time and space. Overall, the dCRY Trp chain has evolutionary importance for light sensing, and its manipulation has implications for optogenetic applications of CRYs.
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