The molecular basis of allostery in a facilitated dissociation process

Facilitated dissociation provides a mechanism by which high-affinity complexes can be rapidly disassembled. The negative feedback regulator CITED2 efficiently downregulates the hypoxic response by displacing the hypoxia-inducible transcription factor HIF-1α from the TAZ1 domain of the transcriptional coactivators CREB-binding protein (CBP) and p300. Displacement occurs by a facilitated dissociation mechanism involving a transient ternary intermediate formed by binding of the intrinsically disordered CITED2 activation domain to the TAZ1:HIF-1α complex. The short lifetime of the intermediate precludes straightforward structural investigations. To obtain insights into the molecular determinants of facilitated dissociation, we model the ternary intermediate by generating a fusion peptide composed of the primary CITED2 and HIF-1α binding motifs. X-ray crystallographic and NMR studies of the fusion peptide complex reveal TAZ1-mediated negative cooperativity that results in nearly mutually exclusive binding of specific CITED2 and HIF-1α interaction motifs, providing molecular-level insights into the allosteric switch that terminates the hypoxic response. [Display omitted] •Mechanistic insights into regulation of the hypoxic response•Molecular determinants for displacement of HIF-1α by facilitated dissociation•Fusion protein strategy to characterize a model of a transient ternary complex•Structural analysis of a negative allosteric network involving disordered proteins The transcriptional response to hypoxia is regulated by a pair of disordered proteins, HIF-1α and CITED2. CITED2 downregulates HIF-1α-mediated transcription by competing for a shared molecular target by facilitated dissociation. Appling et al. model the intermediate of this process using a fusion peptide comprising HIF-1α and CITED2 binding motifs.