Small Peptide inhibitors of acetyl-Peptide hydrolase having an uncommon mechanism of inhibition and a stable bent conformation.

Acyl peptide hydrolase (APEH) catalyzes the removal of acetyl- amino acids from the N-terminus of peptides and cytoplasmic proteins. Due to the role played in several diseases, and to the growing interest around N-terminal acetylation, studies on APEH structure, function, and inhibition are attracting an ever increasing attention. We have therefore screened a random tetrapeptide library, N-capped with selected groups, and identified a trifluoroacetylated tetrapeptide (CF3-lmph) which inhibits the enzyme with a Ki of 24.0 ± 0.8 ?M. The inhibitor is selective for APEH, shows an uncommon uncompetitive mechanism of inhibition, and in solution adopts a stable bent conformation. CF3-lmph efficiently crosses cell membranes, blocking the cytoplasmic activity of APEH; however, it triggers a mild pro-apoptotic effect as compared to other competitive and noncompetitive inhibitors. The unusual inhibition mechanism and the stable structure make the new compound a novel tool to investigate enzyme functions and a useful scaffold to develop more potent inhibitors.