Light sensitivity of the photoreceptor cryptochrome of the Drosophila circadian clock and its interaction with other clock components

Abstract

Flavoprotein cryptochromes (CRYs) are blue light sensors that regulate the circadian clock in plants and animals. They consist of a highly conserved photolyase homology region (PHR) and a C‐terminal tail extension (CTE) of various sizes. In Drosophila CRY, photoreduction of the PHR bound cofactor FAD triggers conformational changes within CRY, which include undocking of C‐terminal Tail (CTT) helix. The mechanism of FAD photoreduction remains a key question in understanding CRY activation.Four tryptophan residues (W420, W397, W342, W394) mediate electron transfer for flavin photoreduction. We have substituted these residues to both redox‐inert phenylalanine residues (F) and redox‐active tyrosine (Y) residues to tune the light sensitivity of CRY. Light‐sensitivities of the variants correlate well with the extent of conformational change at the CTT. Interestingly, the surface tryptophan W394 is the most indispensable residue because it gates electron transfer from exogenous reductant to the photoreduction chain.In flies, CRY interacts with other signaling proteins of the circadian clock in a light depend‐manner to entrain the 24 hour‐cycle to environmental light. For example, in light CRY binds the protein timeless (TIM) and recruits the E3 ligase jetlag to facilitate TIM degradation. However, the molecular interactions between CRY and TIM are not well understood due to the low stability of this protein complex. We have utilized a chemical cross‐linking strategy to map the interfacing domain in this assembly and stabilize it for future structure study by structural methodsSupport or Funding InformationThis work was supported by grants from the NIH: R01GM054339 (to M.W.Y.) and R35GM122535 (to B.R.C.).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.