A fundamental assumption in targeted protein degradation has been that the target protein must display a recognizable degron — a structural tag that flags it for destruction. New structural and biochemical evidence overturns this assumption for an entire class of cancer-relevant enzymes, potentially unlocking dozens of proteins previously considered undruggable by degrader technologies.
Using cereblon (CRBN)-based molecular glue chemistry, researchers developed a highly selective degrader of KAT2A, a lysine acetyltransferase that cooperates with oncogenic drivers including c-Myc and KMT2A fusion proteins. Cryo-electron microscopy at near-atomic resolution revealed that the molecular glue does not require KAT2A to present a degron motif at all; instead, it exploits a surface-exposed tyrosine residue in an antibody-like recognition mode — a mechanistic first for this class of molecules. Selective KAT2A degradation produced potent suppression of histone H3 lysine 9 acetylation (H3K9Ac), a chromatin mark that sustains oncogenic transcriptional programs, accompanied by strong antiproliferative effects in acute myeloid leukemia (AML) cell lines and measurable in vivo efficacy in a patient-derived xenograft model.
This work is genuinely paradigm-shifting within the targeted degradation field. The PROTAC and molecular glue space has been constrained by the requirement for degron recognition, limiting which proteins could be recruited to E3 ligases like CRBN. Demonstrating that a surface-exposed amino acid can substitute for a canonical degron dramatically expands the theoretical target space — potentially encompassing transcription factor co-activators, scaffolding proteins, and other chromatin regulators long regarded as inaccessible. KAT2A specificity over related KAT family members is particularly noteworthy, as homolog selectivity has been a persistent obstacle. Limitations include the early-stage in vivo data (xenograft, not immune-competent models) and the need to establish whether degron-independent recruitment generalizes efficiently across structurally diverse surface epitopes. Nonetheless, the mechanistic precedent alone makes this a landmark contribution to cancer drug discovery.