Cryptochromes are ubiquitous proteins, central to the regulation of the circadian clock. The majority of cryptochromes are light-sensitive and thus also serve as photoreceptors (for blue or red light). Additionally, some cryptochromes act as photoenzymes able to perform DNA damage repair while others are believed to be sensors of the earth’s magnetic field in migratory birds. Despite their ubiquitousness and the exceptional plurality of their function, the mechanisms governing the transition between resting, signaling or enzymatically-capable states of the cryptochromes are poorly understood.
A wide consortium, led by a team at the National Taiwan University and including members from the University of Osaka (Japan) and the University of Marburg (Germany), the Institut de Biologie Structurale (IBS, Grenoble) and the European Synchrotron Radiation Facility (ESRF, Grenoble), was able to record a molecular movie of the events occurring from 10 nanoseconds and 233 milliseconds after illumination, by a combination of time-resolved serial femtosecond crystallography (TR-SFX) at the Spring-8 Angstrom Compact X-ray Free Electron Laser (SACLA, Japan) and time-resolved in crystallo spectroscopy (TR-icOS) on a new instrument of the icOS lab (jointly operated by the ESRF and the IBS).
Cryptochromes bind a flavin adenosine diphosphate (FAD) cofactor which can absorb a blue-light photon, triggering an ultrafast electron transfer chain. This molecular movie sheds light on the structural events that link the ultrafast electron transfer chain to the large-scale rearrangements and C-terminal disorder observed in the light-signaling state. In particular, the protonation step of the FAD cofactor was identified as the key event committing the cryptochrome towards disorder, and light signaling. Its exact timescale was pinpointed via spectroscopic experiments directly carried-out on crystals. This allowed for the identification of a transient protonation pathway visible in the TR-SFX structural movie, opening on a much slower timescale than that of the electron transfer. This protonation step could also be involved in the mechanism of magnetoreceptions by cryptochromes, by affecting the radical pair formed at the end of the electron transfer chain. Overall, the detailed description of the light signaling pathway brings insight into how cryptochrome might switch between their many functions.
Capturing structural intermediates in an animal-like cryptochrome photoreceptor by time-resolved crystallography. Maestre-Reyna M, Hosokawa Y, Wang PH, Saft M, Caramello N, Engilberge S, Franz-Badur S, Gusti Ngurah Putu EP, Nakamura M, Wu WJ, Wu HY, Lee CC, Huang WC, Huang KF, Chang YK, Yang CH, Fong MI, Lin WT, Yang KC, Ban Y, Imura T, Kazuoka A, Tanida E, Owada S, Joti Y, Tanaka R, Tanaka T, Kang J, Luo F, Tono K, Kiontke S, Korf L, Umena Y, Tosha T, Bessho Y, Nango E, Iwata S, Royant A, Tsai MD, Yamamoto J, Essen LO. Science Advances 2025 ; 11(20):eadu7247. doi : 10.1126/sciadv.adu7247.
Contact : Antoine Royant (IBS/Synchrotron Group)