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The encoding of chemical compounds with amplifiable DNA tags facilitates the discovery of small-molecule ligands for proteins. To investigate the impact of stereo- and regiochemistry on ligand discovery, we synthesized a DNA-encoded library of 670,752 derivatives based on 2-azido-3-iodophenylpropionic acids. The library was selected against multiple proteins and yielded specific ligands. The selection fingerprints obtained for a set of protein targets of pharmaceutical relevance clearly showed the preferential enrichment of ortho-, meta- or para-regioisomers, which was experimentally verified by affinity measurements in the absence of DNA. The discovered ligands included novel selective enzyme inhibitors and binders to tumour-associated antigens, which enabled conditional chimeric antigen receptor T-cell activation and tumour targeting.A DNA-encoded chemical library based on regio- and stereoisomers of phenylalanine has been synthesized and used for affinity-based selections against multiple target proteins. This approach led to the isolation and validation of potent ligands capable of CAR T-cell activation and tumour targeting.

Human CtIP is a decisive factor in DNA double-strand break repair pathway choice by enabling DNA-end resection, the first step that differentiates homologous recombination (HR) from non-homologous end-joining (NHEJ). To coordinate appropriate and timely execution of DNA-end resection, CtIP function is tightly controlled by multiple protein–protein interactions and post-translational modifications. Here, we identify the Cullin3 E3 ligase substrate adaptor Kelch-like protein 15 (KLHL15) as a new interaction partner of CtIP and show that KLHL15 promotes CtIP protein turnover via the ubiquitin-proteasome pathway. A tripeptide motif (FRY) conserved across vertebrate CtIP proteins is essential for KLHL15-binding; its mutation blocks KLHL15-dependent CtIP ubiquitination and degradation. Consequently, DNA-end resection is strongly attenuated in cells overexpressing KLHL15 but amplified in cells either expressing a CtIP-FRY mutant or lacking KLHL15, thus impacting the balance between HR and NHEJ. Collectively, our findings underline the key importance and high complexity of CtIP modulation for genome integrity. CtIP has a key role in DNA double-strand break repair as its role in resecting DNA at the break commits a cell to homologous recombination. Here the authors show that KLHL15 interacts with CtIP and regulates repair by controlling protein turnover.

A versatile and Lipinski‐compliant DNA‐encoded library (DEL), comprising 366 600 glutamic acid derivatives coupled to oligonucleotides serving as amplifiable identification barcodes is designed, constructed, and characterized. The GB‐DEL library, constructed in single‐stranded DNA format, allows de novo identification of specific binders against several pharmaceutically relevant proteins. Moreover, hybridization of the single‐stranded DEL with a set of known protein ligands of low to medium affinity coupled to a complementary DNA strand results in self‐assembled selectable chemical structures, leading to the identification of affinity‐matured compounds. A single‐stranded DNA‐encoded chemical library (DEL) of 366 600 compounds, based on a stereoisomeric scaffold and on a single‐stranded DNA format, allows the isolation of ligands against multiple protein targets. The library can also be hybridized to a complementary DNA strand equipped with a protein binder, in order to generate affinity‐matured ligands.