Sandate, C. R. | bioRxiv Science

bioRxiv2023

Structural insights into viral hijacking of p53 by E6 and E6AP

The E3-ubiquitin ligase E6AP degrades p53 when complexed with the viral protein E6 from human papilloma virus (HPV), which contributes to the transformation of cells in HPV-related cancers. Previous crystal structures of the E6AP-E6-p53 ternary complex have implicated a peptide containing an LxxLL motif from E6AP as the interface between the three proteins. However, the contributions to the ternary complex from the remainder of the E6AP protein remain unknown. We reexamined this complex using cryo-EM and full-length proteins and find additional protein interaction interfaces involving a previously uncharacterized domain of E6AP. Additionally, we observe that the ternary complex forms both 1:1:1 and 2:2:2 stochiometric complexes comprised of E6AP, E6 and p53.

biophysics↗

bioRxiv2019

Protein dynamics regulate distinct biochemical properties of cryptochromes in mammalian circadian rhythms

Circadian rhythms are generated by a transcription-based feedback loop where CLOCK:BMAL1 drive transcription of their repressors (PER1/2, CRY1/2), which bind to CLOCK:BMAL1 to close the feedback loop with ~24-hour periodicity. Here we identify a key biochemical and structural difference between CRY1 and CRY2 that underlies their differential strengths as transcriptional repressors. While both cryptochromes bind the BMAL1 transactivation domain with similar affinity to sequester it from coactivators, CRY1 is recruited with much higher affinity to the PAS domain core of CLOCK:BMAL1, allowing it to serve as a stronger repressor that lengthens circadian period. We identify a dynamic loop in the secondary pocket that regulates differential binding of cryptochromes to the PAS domain core. Notably, PER2 binding remodels this loop in CRY2 to enhance its affinity for CLOCK:BMAL1, explaining why CRY2 forms an obligate heterodimer with PER2, while CRY1 is capable of repressing CLOCK:BMAL1 both with and without PER2.

biochemistry↗