The SUMO1-E67 interacting loop peptide is an allosteric inhibitor of the dipeptidyl peptidases 8 and 9.

The intracellular peptidases dipeptidyl peptidase (DPP) 8 and DPP9 are involved in multiple cellular pathways including antigen maturation, cellular homeostasis, energy metabolism, and cell viability. Previously we showed that the small ubiquitin-like protein modifier SUMO1 interacts with an armlike structure in DPP9, leading to allosteric activation of the peptidase. Here we demonstrate that the E67-interacting loop (EIL) peptide, which corresponds to the interaction surface of SUMO1 with DPP9, acts as a noncompetitive inhibitor of DPP9. Moreover, by analyzing the sensitivity of DPP9 arm mutants to the EIL peptide, we mapped specific residues in the arm that are important for inhibition by the EIL, suggesting that the peptide acts as an allosteric inhibitor of DPP9. By modifying the EIL peptide, we constructed peptide variants with more than a 1,000-fold selectivity toward DPP8 (147 nM) and DPP9 (170 nM) over DPPIV (200 μM). Furthermore, application of these peptides to cells leads to a clear inhibition of cellular prolyl peptidase activity. Importantly, in line with previous publications, inhibition of DPP9 with these novel allosteric peptide inhibitors leads to an increase in EGF-mediated phosphorylation of Akt. This work highlights the potential use of peptides that mimic interaction surfaces for modulating enzyme activity.