Difference between revisions of "Part:BBa K4874002"

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BIC2-CDS

BIC2-CDS

Profile

Name: BIC2-CDS

Base Pairs: 351 bp

Origin: the homodimeric plant, Synthetic

Properties: BIC2 is a factor that inhibits CRY2 activation.

Usage and Biology

BICs play two roles in CRY2 inhibition. On the one hand, BIC2 inhibits the photoreduction of CRY2. The binding of BIC2 does not alter the overall structure of the CRY2 PHR or FAD binding, but increases the distance between FAD and residues in the electron transfer pathway and rotates the side chain of the proton donor, D393, by approximately 52°, yielding a longer d (HD393-N5ISO). Given the important role of D393 in the photoresponse, the researchers suggest that this alteration may prevent the protonation of FAD by D393, thereby interfering with the blue-light-dependent photoresponse of CRY2[1].

On the other hand, BICs inhibit the oligomerization of light-activated CRY2 and its interactions with signaling chaperones. The PHR structural domains of CRYs mediate oligomerization and interactions with CIBs. In addition, BICs appear to prevent blue-light-dependent conformational changes in the CRY PHR structural domain. Blue light has been reported to cause a significant loss of β-folding in the α/β subregion of Chlamydomonas photolyase homolog 1 PHR43. In the structure of our BIC2-CRY2N complex, BIC2 displays a "U-shaped lock" structure in which helix 1 and helix 4 in BIC2 mainly contact the α and α/β subdomains of PHR, respectively. This lock structure can tightly stabilize the conformation of the CRY2 PHR domain [1].

Firstly, BIC2 presents as an extremely extended structure, meandering around CRY2 a/b and the groove between the structural domains, forming extensive hydrogen bonding and hydrophobic interactions with CRY2. This extensive interaction may occupy the oligomerization site of CRY2 thus inhibiting the blue-light-mediated oligomerization of CRY2, and also be able to promote the depolymerization of CRY2 oligomers to keep them in the monomeric state; moreover, BIC2 can block the interaction of CRY2 oligomers with the downstream transcription factor CIB1 thus blocking blue-light signaling. Secondly, BIC2 inhibited the photoreduction of FAD, a chromogenic molecule in CRYs proteins. During photoreduction, FAD accepts an external electron to change into FAD--, and D393 of CRY2 provides a proton to change FAD-- into FADH-. Through molecular simulation, it was found that the binding of BIC2 lengthens the path of electron and proton transfer, thus hindering electron and proton transfer and inhibiting the photoreduction of FAD. In addition, the regions where BICs interact with CRYs proteins were also found to be very conserved in different plant species by sequence comparison, predicting that this inhibition mechanism is generally applicable in plants[2].

References

[1]Ma, L., Guan, Z., Wang, Q., Yan, X., Wang, J., Wang, Z., … Yin, P. (2020). Structural insights into the photoactivation of Arabidopsis CRY2. Nature Plants. doi:10.1038/s41477-020-00800-1.

[2]Ma, L., Wang, X., Guan, Z. et al. Structural insights into BIC-mediated inactivation of Arabidopsis cryptochrome 2. Nat Struct Mol Biol 27, 472–479 (2020). https://doi.org/10.1038/s41594-020-0410-z.

Sequence and Features