Exploring the Conformational Landscape of the Neh4 and Neh5 Domains of Nrf2 Using Two Different Force Fields and Circular Dichroism.

The nuclear factor erythroid 2-related factor 2 (Nrf2)-ARE transcriptional response pathway plays a critical role in protecting the cell from oxidative stresses via the upregulation of cytoprotective genes. Aberrant activation of Nrf2 in cancer cells can confer this cytoprotectivity, thereby reducing the efficacy of both chemotherapeutics and radiotherapies. Key to this antioxidant pathway is the interaction between Nrf2 and CREB binding protein (CBP), mediated by the Neh4 and Neh5 domains of Nrf2. Disruption of this interaction via small-molecule therapeutics could negate the effects of aberrant Nrf2 upregulation. Due to the disordered nature of these domains, there remains no three-dimensional structure of Neh4 or Neh5, making structure-based drug design a challenge. Here, we performed 48 μs of unbiased molecular dynamics (MD) simulations with the Amber99SB*-ILDNP and CHARMM36m force fields and circular dichroism (CD) spectropolarimetry experiments to elucidate the free-state structures of these domains; no previous data regarding their conformational landscapes exists. There are two main findings: First, we find Neh5 to be markedly more disordered than Neh4, which has nine residues in the middle of the domain showing α-helical propensity, thus pointing to Neh4 and Neh5 having different binding mechanisms. Second, the two force fields show strong differences for the glutamic acid-rich Neh5 peptide but are in reasonable agreement for Neh4, which has no glutamic acid. The CHARMM36m force field agrees more closely with the CD results.