N-terminal sequences are important sites for post-translational modifications that alter protein localization, activity, and stability. Dipeptidyl peptidase 9 (DPP9) is a serine aminopeptidase with the rare ability to cleave off N-terminal dipeptides with imino acid proline in the second position. Here, we identify the tumor-suppressor BRCA2 as a DPP9 substrate and show this interaction to be induced by DNA damage. We present crystallographic structures documenting intracrystalline enzymatic activity of DPP9, with the N-terminal Met1-Pro2 of a BRCA21-40 peptide captured in its active site. Intriguingly, DPP9-depleted cells are hypersensitive to genotoxic agents and are impaired in the repair of DNA double-strand breaks by homologous recombination. Mechanistically, DPP9 targets BRCA2 for degradation and promotes the formation of RAD51 foci, the downstream function of BRCA2. N-terminal truncation mutants of BRCA2 that mimic a DPP9 product phenocopy reduced BRCA2 stability and rescue RAD51 foci formation in DPP9-deficient cells. Taken together, we present DPP9 as a regulator of BRCA2 stability and propose that by fine-tuning the cellular concentrations of BRCA2, DPP9 alters the BRCA2 interactome, providing a possible explanation for DPP9's role in cancer.
Dipeptidyl peptidase 9 (DPP9) is a serine protease cleaving N-terminal dipeptides preferentially post-proline with (patho)physiological roles in the immune system and cancer. Only few DPP9 substrates are known. Here we identify an association of human DPP9 with the tumour suppressor BRCA2, a key player in repair of DNA double-strand breaks that promotes the formation of RAD51 filaments. This interaction is triggered by DNA-damage and requires access to the DPP9 active-site. We present crystallographic structures documenting the N-terminal Met1-Pro2 of a BRCA21-40 peptide captured in the DPP9 active-site. Mechanistically, DPP9 targets BRCA2 for degradation by the N-degron pathway, and promotes RAD51 foci formation. Both processes are phenocopied by BRCA2 N-terminal truncation mutants, indicating that DPP9 regulates both stability and the cellular stoichiometric interactome of BRCA2. Consistently, DPP9-deprived cells are hypersensitive to DNA-damage. Together, we identify DPP9 as a regulator of BRCA2, providing a possible explanation for DPP9 involvement in cancer development.
Representative scheme of DPP4N_Peptidase_S9 structure and an image from PDBsum server
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6QZV Previously Class, Architecture, Topology and Homologous superfamily - PDB-Sum server
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6QZVFold classification based on Structure-Structure alignment of Proteins - FSSP server
