Cry2

Cry2, short for cryptochrome-2, is a blue-light photoreceptor and a core component of the circadian clock in many organisms. It belongs to the cryptochrome/photolyase family, proteins homologous to DNA repair enzymes but generally lacking DNA repair activity in their cryptochrome form. The CRY2 protein is encoded by the CRY2 gene and exists alongside other cryptochromes such as CRY1 in animals and plants, where it participates in light signaling and timing pathways.

In terms of structure, CRY2 contains a photolyase-like domain that binds a flavin adenine dinucleotide (FAD) cofactor and a C-terminal tail that mediates interactions with other clock or signaling proteins. In plants, CRY2 is actively responsive to blue light; upon illumination, it undergoes conformational changes and translocates or interacts with transcriptional regulators to adjust gene expression related to photomorphogenesis, seedling development, and flowering time. In vertebrates, including humans, CRY2 is a key component of the transcriptional-translational feedback loop that sustains circadian rhythms. It acts primarily as a repressor of the CLOCK-BMAL1 complex, often in concert with PER proteins, to regulate the expression of clock-controlled genes. Mammalian CRY2 is considered to be light-insensitive in a direct sense, with light entrainment mediated by other retinal photoreceptors, while CRY2 nonetheless maintains essential clock functions in the brain and peripheral tissues.

CRY2 activity is modulated by post-translational modifications, including phosphorylation and interactions with ubiquitin ligases such as FBXL3, which influence CRY2 stability and turnover. Genetic variation in CRY2 has been studied for associations with circadian traits, metabolic regulation, and susceptibility to mood or sleep disorders, though findings are ongoing and context-dependent.

Overall, CRY2 serves as a conserved sensor and regulator linking environmental cues to internal timing mechanisms across species.