Defects in transcriptional regulation are prominent in human disease. For instance, dysregulation in the protein-protein interaction (PPI) network of transcriptional components, such as activators and coactivators, can profoundly affect gene expression. Activators bind to the genome to promote expression at specific genes, while coactivators establish a bridge of communication between activators and the general transcription machinery. In this way, coactivators and activators play a protagonist role during transcription initiation. Thus, inhibiting coactivator-activator PPIs is an avenue to modulate gene expression, and can provide mechanistic insight as well as highlight the value of targeting transcriptional components for therapeutic development. Synthetic molecules are a potential resource to inhibit these PPIs, and molecules that selectively engage coactivator-activator complexes in vitro and in cells are key for understanding their role in disease processes. Here, we report the development of a target-adjustable inhibitor of activator-coactivator complexes based on a natural product lipopeptide previously discovered by the Mapp and Sherman labs. Structure-activity relationship studies of this inhibitor demonstrate adjustability in the selectivity of lipopeptide analogs for various coactivators, including Med25 and CBP/p300. Using fluorescence polarization binding assays, we identified specific lipopeptide residues that dictate the selective disruption of coactivator-activator PPIs. Additionally, the mode of binding of potent inhibitors to their main target was determined using HSQC. Our results suggest the occurrence of specific interactions between lipopeptide residues and coactivators, which are in turn important contributors to the inhibitory activity and selectivity of the lipopeptide analogs. Our data positions this lipopeptide as a chemical scaffold with modifiable selectivity, and it informs the development of a chemical probe for the characterization of dysregulated coactivator PPI networks.

Development of a coactivator-activator PPI inhibitor with modifiable target selectivity

ACS Spring 2022

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