Disruption of R2TP-mediated PIKK maturation with de novo designed binders
Phosphatidylinositol 3-kinase-related kinases (PIKKs), including ATM, ATR, DNA-PKcs, SMG1, TRRAP and mTOR, are regulators of gene expression, DNA damage response and metabolism. Their maturation depends on R2TP, a co-chaperone complex comprising the RUVBL1/2 AAA+ ATPase, RPAP3 and PIH1D1. While small-molecule RUVBL1/2 inhibitors have shown promise in cancer models, the presence of RUVBL1/2 in other complexes raises concerns about specificity. Here, we identified the RUVBL1/2-RPAP3 interface as a vulnerability, exploiting it using de novo designed protein binders that occupy the RPAP3-binding site. These subnanomolar-affinity binders dismantle R2TP, depleting levels of all PIKKs while sparing other RUVBL1/2-containing complexes, including chromatin remodelers INO80, SRCAP and TIP60. CryoEM, proteomic, biochemical and cellular analyses revealed that these binders outcompete RPAP3, trapping RUVBL1/2 in a catalytically inactive conformation. Our findings establish selective disruption of R2TP by artificial proteins as a strategy to control PIKK abundance.