Project description:Site-specific DNA binding by proteins is critical for regulating genetic activity and cell fate decision. However, identifying proteins bound to specific genomic regions (e.g., promoter or enhancer) remains challenging. To address this, we developed the Site-specific non-canonical amino acid resolved Protein EnRichment (SUPER) system, incorporating a photo-crosslinking amino acid into nuclease-deficient dCas9 mutant. Human pluripotent stem cells (hPSCs) carrying SUPER enables the capture of proteins bound to, in theory, any genomic location, facilitating the study of the cell context-dependent DNA-protein interactions. Using SUPER, we identified OCT4/SOX2/CARHSP1 complex binding to the NANOG promoter to maintain pluripotency in hPSCs. During ectoderm differentiation, ZIC2 acts as a competitive inhibitor, binding the same promoter to downregulate NANOG expression and promote differentiation. Additionally, SUPER identified ZNF8 binding to the distal regulatory region of OCT4 and maintain naïve pluripotency. In summary, SUPER provides a robust system for uncovering the cell context-dependent, site-specific genome regulators, offering valuable insights into gene regulation networks driving cell fate transitions.
Project description:Site-specific DNA binding by proteins is critical for regulating genetic activity and cell fate decision. However, identifying proteins bound to specific genomic regions (e.g., promoter or enhancer) remains challenging. To address this, we developed the Site-specific non-canonical amino acid resolved Protein EnRichment (SUPER) system, incorporating a photo-crosslinking amino acid into nuclease-deficient dCas9 mutant. Human pluripotent stem cells (hPSCs) carrying SUPER enables the capture of proteins bound to, in theory, any genomic location, facilitating the study of the cell context-dependent DNA-protein interactions. Using SUPER, we identified OCT4/SOX2/CARHSP1 complex binding to the NANOG promoter to maintain pluripotency in hPSCs. During ectoderm differentiation, ZIC2 acts as a competitive inhibitor, binding the same promoter to downregulate NANOG expression and promote differentiation. Additionally, SUPER identified ZNF8 binding to the distal regulatory region of OCT4 and maintain naïve pluripotency. In summary, SUPER provides a robust system for uncovering the cell context-dependent, site-specific genome regulators, offering valuable insights into gene regulation networks driving cell fate transitions.
Project description:The coxibs are a subset of non-steroidal anti-inflammatory drugs (NSAIDs) that selectively target cyclooxygenase-2 (COX-2) to inhibit prostaglandin signaling and reduce inflammation. However, only celecoxib remains in use, necessitating exploration of broader mechanisms of the coxibs. Here, we report a novel binding site for celecoxib on prostaglandin E synthase (PTGES), an enzyme downstream of COX-2 in the prostaglandin signaling pathway using an isotopically-coded cleavable chelation-assisted biotin probe. Evaluation of the multi-functional probe revealed significantly improved tagging efficiencies attributable to promotion of CuAAC chemistry by the embedded picolyl functional group. Application of the probe within the small molecule interactome mapping by photo-affinity labeling (SIM-PAL) platform using photo-celecoxib as a reporter for celecoxib identified known targets (e.g., carbonic anhydrase 12) and the significant enrichment of PTGES, along with six additional membrane proteins and 15 subunits of the cytochrome complex. In addition, four binding sites to celecoxib were mapped by the probe, including a direct interaction with PTGES. The interaction between celecoxib and PTGES was validated by competitive displacement and thermal shift assay. The binding site between celecoxib and PTGES enabled the development of a structural model of the interaction and will inform the further development of new selective inhibitors of the prostaglandin signaling pathway.
Project description:The super elongation complex (SEC) contains the positive transcription elongation factor b (P-TEFb) and a subcomplex, ELL2-EAF1, which stimulates transcription elongation by RNA polymerase II (Pol II). Here we report the cryo-EM structure of ELL2-EAF1 bound to a Pol II elongation complex at 2.8 Å resolution. The ELL2-EAF1 dimerization module directly binds the Pol II lobe, explaining how SEC delivers P-TEFb to Pol II. The same site on the lobe also binds the initiation factor TFIIF, consistent with SEC binding only after the transition from transcription initiation to elongation. Structure-guided functional analysis shows that elongation stimulation requires the dimerization module and an ELL2 protein linker that tethers this module to the Pol II protrusion. Our results show that SEC stimulates elongation allosterically and indicate that this stimulation involves stabilization of a further closed conformation of the Pol II active center cleft.