Induced ubiquitination of the partially disordered Estrogen Receptor alpha protein via a 14-3-3-directed molecular glue-based PROTAC design

Proteins lacking defined ligandable pockets remain challenging drug targets. Here, we develop a molecular glue-based PROTAC (MGPROTACs) approach that chemically conjugates a molecular glue stabilizer to a VHL-recruiting ligand to capture and ubiquitinate the 14-3-3/Estrogen Receptor (ER) complex. Our designed MGPROTACs engage a composite interface between 14-3-3 and the disordered F-domain of ER, promoting cooperative complex formation and target ubiquitination. Biophysical characterization revealed distinct linker-dependent cooperativities across the MGPROTAC series, which influenced both cellular permeability and ubiquitination efficiency. Cryo-EM of the most cooperative MGPROTAC uncovers de novo VHL-14-3-3{zeta} contacts, while molecular dynamics simulations rationalize the stabilizing interactions underlying cooperativity. Strikingly, fine-tuning linker design enables selective ubiquitination of distinct complex subunits. These findings establish a structural and mechanistic framework for integrating molecular glue and PROTAC principles, expanding the scope of drug discovery to previously intractable protein complexes.