Evaluation of the steric impact of flavin adenine dinucleotide in Drosophila melanogaster cryptochrome function

•FAD improves overall cryptochrome motility, decreasing rigidity even in darkness.•Ser526 phosphorylation is found to enhance C-terminal tail conformational change.•The C-terminal FFW motif is found to mimic the DNA position in (6–4) photolyases.•Mechanistic insights help explain cryptochrome activation upon light exposure. Photoreceptors are crucial components for circadian rhythm entrainment in animals, plants, fungi and cyanobacteria. Cryptochromes (CRYs) are flavin adenine dinucleotide (FAD) containing photoreceptors, and FAD is responsible for signal transduction, in contrast to photolyases where it promotes DNA-damage repair. In this work, we investigated an alternative role for FAD in CRY. We analyzed the Drosophila melanogaster CRY crystal structure by means of molecular dynamics, elucidating how this large co-factor within the receptor could be crucial for CRY structural stability. The co-factor appears indeed to improve receptor motility, providing steric hindrance. Moreover, multiple sequence alignments revealed that conserved motifs in the C-terminal tail could be necessary for functional stability.