The molecular glue CLEO4-88 inhibits the ACAA1 thiolase by induced binding to GID4

Molecular glues promote protein-protein interactions by enhancing the surface complementarity between proteins. Those that recruit an E3 ubiquitin ligase to a target can elicit ubiquitination and subsequent destruction of the target protein-a mechanism that underpins the field of targeted protein degradation (TPD). Here we explored whether small-molecule binders to the CTLH E3 ligase subunit GID4 could act as molecular glues. We discovered that CLEO4-88 functions as a molecular glue (EC₅₀ = 12.5 nM) to promote the interaction of GID4 with the peroxisomal thiolase ACAA1 in vitro and in cellulo. An atomic structure of the ternary complex revealed an allosteric mechanism whereby CLEO4-88 binds solely to GID4 and induces a conformational change conducive to binding ACAA1. Biochemical analysis demonstrated that, while ACAA1 cannot be recruited by GID4 to a CTLH holoenzyme for ubiquitination, ternary complex formation inhibits ACAA1 thiolase activity, thus demonstrating potential utility beyond TPD.