Structure of full-length Drosophila cryptochrome

Area of Science:

• Biochemistry
• Structural Biology
• Photobiology

Background:

• The cryptochrome/photolyase (CRY/PL) family are essential photoreceptors involved in DNA repair and light-mediated signaling across all life forms.
• While photolyases repair DNA damage from UV radiation, cryptochromes regulate crucial processes like circadian rhythms, growth, development, and magnetosensitivity.
• Despite functional divergence, CRYs and PLs share a conserved structural fold, flavin adenine dinucleotide (FAD) dependence, and an internal photoactivation mechanism.

Purpose of the Study:

• To elucidate the structural basis of animal cryptochrome function, particularly how it interacts with substrates.
• To investigate the role of the C-terminal tail in cryptochrome activity and its relationship to the photolyase homology domain (PHD).
• To understand the mechanism by which conserved protein architecture and photochemistry enable diverse light-driven functions within the CRY/PL family.

Main Methods:

• X-ray crystallography was employed to determine the high-resolution (2.3 Å) structure of Drosophila CRY, including its intact C terminus.
• Structural analysis focused on the interaction of the C-terminal helix with the catalytic core and comparison with DNA-binding sites in photolyases.
• Conformational analysis of the flavin adenine dinucleotide (FAD) cofactor within the CRY structure was performed.

Main Results:

• The crystal structure reveals that the C-terminal helix of Drosophila CRY occupies a groove analogous to the DNA-binding site in photolyases.
• A conserved tryptophan residue (Trp536) is positioned within the CRY catalytic center, mimicking the interaction of photolyases with DNA photolesions.
• The observed conformation of the FAD anionic semiquinone suggests its role in facilitating the restructuring of the C-terminal tail helix.

Conclusions:

• The structure of Drosophila CRY provides a mechanistic explanation for how a conserved protein fold and photochemistry are adapted for diverse functions, such as circadian regulation.
• The findings reconcile the distinct roles of CRYs and PLs by demonstrating how structural elements like the C-terminal tail mediate substrate recognition and signaling.
• This study advances our understanding of light-driven biological processes and the evolutionary adaptability of the CRY/PL photoreceptor family.