Crystallographic fragment screening of CDK2-cyclin A: FragLites map sites of protein-protein interaction.

Sites of protein-protein interaction (PPI) are potentially more selective binding sites for therapeutics than protein substrate-binding sites. PPIs include distinct regions frequently called "hotspots," sites of key amino acid interactions. Prospective identification of these hotspots through X-ray crystallographic screening could assist in the identification of separation of function mutants for experimental validation, enhance confidence in AI-generated multiprotein complex predictions, and accelerate development of selective chemical probes. To explore these applications, we utilize the FragLite library to examine the binding surfaces of CDK2-cyclin A. The many protein- and peptide-CDK2-cyclin A complexes that have been structurally characterized make this complex an appropriate test case. We show that FragLites comprehensively map both known sites of protein-protein interaction on CDK2-cyclin A and identify a possible uncharacterized site, providing a structural method toward directing mechanistic studies and starting points for chemical probe design.