Dynamics of mechanism of a dual function of DNA repair and signal transduction by CraCRY protein

The cryptochrome/photolyase family (CPF) is a group of structurally similar flavoproteins with distinct functions. The function of photolyases (PLs) is to repair DNA lesion caused by ultraviolet radiation. Cryptochromes (CRYs) exhibit various functions, serving as blue-light photoreceptors in plants and insects, regulating their growth and development. Most CRYs do not possess DNA repair functions. However, a recently discovered animal-like cryptochrome named CraCRY in Chlamydomonas reinhardtii functions as both cryptochrome and (6-4) photolyase, which can repair a type of DNA lesion caused by ultraviolet light, (6-4) photoproduct (6-4PP). The molecular mechanism by which CraCRY utilizes blue light energy to repair DNA lesion and form the initial signaling state remains unclear. Here, we used ultrafast spectroscopy and single-molecule methods to elucidate the dynamics and molecular mechanism of CraCRY. We elucidate the entire repair photocycle with femtosecond resolution and the structural conformation of initial signaling with single-molecule detection. We also reveal the actual redox state for simultaneously maintaining the two functions, which is a hot debate of the key cofactor issue in the field.