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Current methods for proteomimetic engineering rely on structure‐based design. Here we describe a design strategy that allows the construction of proteomimetics against challenging targets without a priori characterization of the target surface. Our approach employs (i) a 100‐membered photoreactive foldamer library, the members of which act as local surface mimetics, and (ii) the subsequent affinity maturation of the primary hits using systems chemistry. Two surface‐oriented proteinogenic side chains drove the interactions between the short helical foldamer fragments and the proteins. Diazirine‐based photo‐crosslinking was applied to sensitively detect and localize binding even to shallow and dynamic patches on representatively difficult targets. Photo‐foldamers identified functionally relevant protein interfaces, allosteric and previously unexplored targetable regions on the surface of STAT3 and an oncogenic K‐Ras variant. Target‐templated dynamic linking of foldamer hits resulted in two orders of magnitude affinity improvement in a single step. The dimeric K‐Ras ligand mimicked protein‐like catalytic functions. The photo‐foldamer approach thus enables the highly efficient mapping of protein‐protein interaction sites and provides a viable starting point for proteomimetic ligand development without a priori structural hypotheses. [ABSTRACT FROM AUTHOR]

Flat protein surfaces involved in protein– protein interactions are notoriously difficult targets. In theirResearch Article ( e202410435), Tamás A. Martinek, György M. Keserű et al. addressed this challenge by creating a protein surface- compatible library of short helical foldamers that can be used as fragments. The light- induced photoscreening enabled the capture and localization of the weak binding of the helices to the target. Protein- templated linking of the initial hits to dimeric compounds increased their affinity and resulted in functional proteomimetics. [Extracted from the article]