Isoform-selective regulation of mammalian cryptochromes

The tail of cryptochromes: an intrinsically disordered cog within the mammalian circadian clock

“…Identifying the autoinhibitory function of exon 11 and a molecular rationale for CRY1Δ11-mediated delayed sleep phase disorder should motivate the development of inhibitors that modulate the CRY1/ CLOCK interaction at the secondary pocket to restore normal circadian timing (and sleep onset) or reset circadian rhythms [24,35]. Conversely, small molecule ligands that target the FAD-binding pocket to modulate circadian rhythms also appear to suggest an important functional role for CRY tails near the FAD-binding pocket [37].…”

“…c A possible model for how the tail (magenta) might bind to both the FAD-binding pocket and the secondary pocket on the PHR domain in the absence of PER proteins. Exon 10 has been implicated at binding near the FAD-binding pocket [37], while exon 11 inhibits CLOCK PAS-B binding at the secondary pocket and deletion of exon 12 has no effect on affinity of the tail for the PHR domain [35] These findings are consistent with the emerging model that tighter binding of CRY leads to a longer circadian period [30]. Because the mutant allele directly modifies only the intrinsically disordered C-terminal tail, and not the PHR domain where cryptochromes have been shown to directly interact with CLOCK:BMAL1, these data suggest that loss of exon 11 relieves some type of autoinhibitory role of the tail between the CRY1 PHR domain and CLOCK:BMAL1, thus making CRY1Δ11 a more effective repressor.…”

“…The circadian clock can be modulated by small molecules that rely on CRY tails Nearly a decade ago, cryptochromes entered the chemical biology arena with the discovery of KL001, a small molecule that stabilizes CRY half-life by occupying the FAD-binding pocket of CRY to compete with binding of the ubiquitin ligase FBXL3 [10,56,57]. More recently, Hirota and colleagues identified two new molecules that target CRY1 or CRY2 to extend circadian period by selectively extending the half-life of their respective target [37]. Although they similarly bind to the highly conserved FAD-binding pocket of their respective CRY targets, both small molecules require the intrinsically disordered tails for selectivity and the stabilization of cryptochromes in cells [37].…”

“…More recently, Hirota and colleagues identified two new molecules that target CRY1 or CRY2 to extend circadian period by selectively extending the half-life of their respective target [37]. Although they similarly bind to the highly conserved FAD-binding pocket of their respective CRY targets, both small molecules require the intrinsically disordered tails for selectivity and the stabilization of cryptochromes in cells [37]. To identify how the tails contribute to selectivity, chimeras swapping regions of the tail between CRY1 and CRY2 revealed that the PHR domain-proximal exon 10 is required for selectivity in cells [37].…”

“…Although they similarly bind to the highly conserved FAD-binding pocket of their respective CRY targets, both small molecules require the intrinsically disordered tails for selectivity and the stabilization of cryptochromes in cells [37]. To identify how the tails contribute to selectivity, chimeras swapping regions of the tail between CRY1 and CRY2 revealed that the PHR domain-proximal exon 10 is required for selectivity in cells [37]. Given that the molecules target the FADbinding pocket on the opposite side of the PHR domain from the secondary pocket, these data suggest that the short, linear binding motifs identified in exons 10 and 11 may target discrete sites on the PHR domain (Fig.…”