Trp-Arg-Xaa tripeptides act as uncompetitive-type inhibitors of human dipeptidyl peptidase IV

•A Trp-Arg-Xaa tripeptides library was analyzed to develop hDPPIV inhibitor.•Trp-Arg-Glu showed the highest inhibitory effect against hDPPIV.•All of the tested 19 Trp-Arg-Xaa tripeptides showed uncompetitive-type inhibition. Human dipeptidyl peptidase IV (hDPPIV, alternative name: CD26) inhibitors provide an effective strategy for the treatment of type 2 diabetes. Recently, our research group discovered a non substrate-mimic inhibitory dipeptide, Trp-Arg, by the systematic analysis of a dipeptide library. In the present study, a tripeptide library Trp-Arg-Xaa (where Xaa represents any amino acid) was analyzed to investigate the interactions of peptidergic inhibitors with hDPPIV. Trp-Arg-Glu showed the highest inhibitory effect toward hDPPIV (Ki=130μM). All of the tested 19 Trp-Arg-Xaa tripeptides showed unique uncompetitive-type inhibition. The inhibition mechanism of Trp-Arg-Xaa is discussed based on the crystal structure of hDPPIV. The information obtained by this study suggests a novel concept for developing hDPPIV inhibitory peptides and drugs.