Changes

Although Charles Darwin first documented plant responses to blue light in the 1800s, it was not until the 1980s that research began to identify the pigment responsible.[9] In 1980, researchers discovered that the HY4 gene of the plant Arabidopsis thaliana was necessary for the plant's blue light sensitivity, and, when the gene was sequenced in 1993, it showed high sequence homology with photolyase, a DNA repair protein activated by blue light. By 1995, it became clear that the products of the HY4 gene and its two human homologs did not exhibit photolyase activity and were instead a new class of blue light photoreceptor hypothesized to be circadian photopigments. In 1996 and 1998, Cry homologs were identified in Drosophila and mice, respectively.

The structure of cryptochrome involves a fold very similar to that of photolyase, with a single molecule of FAD noncovalently bound to the protein.[8] These proteins have variable lengths and surfaces on the C-terminal end, due to the changes in genome and appearance that result from the lack of DNA repair enzymes. The Ramachandran plot shows that the secondary structure of the CRY1 protein is primarily a right-handed alpha helix with little to no steric overlap.[16] The structure of CRY1 is almost entirely made up of alpha helices, with several loops and few beta sheets. The molecule is arranged as an orthogonal bundle.