A putative flavin electron transport pathway is differentially utilized in Xenopus CRY1 and CRY2

Area of Science:

• Chronobiology
• Molecular Biology
• Biochemistry

Background:

• Vertebrate circadian rhythms are regulated by the CLOCK/BMAL1 transcriptional feedback loop.
• Xenopus laevis cryptochromes (xCRYs) act as negative regulators in this circadian oscillator.
• Cryptochromes, like photolyases, possess a conserved flavin-binding domain essential for their function.

Purpose of the Study:

• To investigate the role of the flavin-binding domain in xCRY function.
• To elucidate molecular and biochemical differences between xCRY1 and xCRY2.
• To determine the necessity of the putative electron transport chain in xCRY activity.

Main Methods:

• Site-directed mutagenesis of conserved tryptophan residues in xCRY1 and xCRY2b.
• Functional assays measuring the suppression of CLOCK/BMAL1-mediated promoter activation.
• Biochemical analysis of flavin binding and electron transport capabilities.

Main Results:

• An intact flavin-binding domain is essential for both xCRY1 and xCRY2b function.
• Mutations in the conserved tryptophan residues differentially affect xCRY1 and xCRY2b activity.
• xCRY2b function is inhibited by mutations in any of the three conserved tryptophans, while xCRY1 is only significantly affected by mutation in the last tryptophan.

Conclusions:

• This study demonstrates the first molecular/biochemical differences between xCRY1 and xCRY2.
• Both xCRYs require flavin binding, suggesting the importance of electron transport in their function.
• xCRY2b's function is dependent on electron transport via the conserved tryptophan pathway, unlike xCRY1.